diff --git a/client/block-builder/src/lib.rs b/client/block-builder/src/lib.rs
index a4c6f5aad2aeb..3f9fecbccbb9e 100644
--- a/client/block-builder/src/lib.rs
+++ b/client/block-builder/src/lib.rs
@@ -35,6 +35,7 @@ use sp_blockchain::{ApplyExtrinsicFailed, Error};
 use sp_core::ExecutionContext;
 use sp_runtime::{
 	generic::BlockId,
+	legacy,
 	traits::{Block as BlockT, Hash, HashFor, Header as HeaderT, NumberFor, One},
 	Digest,
 };
@@ -135,6 +136,7 @@ where
 pub struct BlockBuilder<'a, Block: BlockT, A: ProvideRuntimeApi<Block>, B> {
 	extrinsics: Vec<Block::Extrinsic>,
 	api: ApiRef<'a, A::Api>,
+	version: u32,
 	block_id: BlockId<Block>,
 	parent_hash: Block::Hash,
 	backend: &'a B,
@@ -183,10 +185,15 @@ where
 
 		api.initialize_block_with_context(&block_id, ExecutionContext::BlockConstruction, &header)?;
 
+		let version = api
+			.api_version::<dyn BlockBuilderApi<Block>>(&block_id)?
+			.ok_or_else(|| Error::VersionInvalid("BlockBuilderApi".to_string()))?;
+
 		Ok(Self {
 			parent_hash,
 			extrinsics: Vec::new(),
 			api,
+			version,
 			block_id,
 			backend,
 			estimated_header_size,
@@ -199,13 +206,26 @@ where
 	pub fn push(&mut self, xt: <Block as BlockT>::Extrinsic) -> Result<(), Error> {
 		let block_id = &self.block_id;
 		let extrinsics = &mut self.extrinsics;
+		let version = self.version;
 
 		self.api.execute_in_transaction(|api| {
-			match api.apply_extrinsic_with_context(
-				block_id,
-				ExecutionContext::BlockConstruction,
-				xt.clone(),
-			) {
+			let res = if version < 6 {
+				#[allow(deprecated)]
+				api.apply_extrinsic_before_version_6_with_context(
+					block_id,
+					ExecutionContext::BlockConstruction,
+					xt.clone(),
+				)
+				.map(legacy::byte_sized_error::convert_to_latest)
+			} else {
+				api.apply_extrinsic_with_context(
+					block_id,
+					ExecutionContext::BlockConstruction,
+					xt.clone(),
+				)
+			};
+
+			match res {
 				Ok(Ok(_)) => {
 					extrinsics.push(xt);
 					TransactionOutcome::Commit(Ok(()))
diff --git a/client/rpc/src/state/tests.rs b/client/rpc/src/state/tests.rs
index 9dbe02cdb7d64..287dfac8c6ba0 100644
--- a/client/rpc/src/state/tests.rs
+++ b/client/rpc/src/state/tests.rs
@@ -527,7 +527,7 @@ fn should_return_runtime_version() {
 
 	let result = "{\"specName\":\"test\",\"implName\":\"parity-test\",\"authoringVersion\":1,\
 		\"specVersion\":2,\"implVersion\":2,\"apis\":[[\"0xdf6acb689907609b\",4],\
-		[\"0x37e397fc7c91f5e4\",1],[\"0xd2bc9897eed08f15\",3],[\"0x40fe3ad401f8959a\",5],\
+		[\"0x37e397fc7c91f5e4\",1],[\"0xd2bc9897eed08f15\",3],[\"0x40fe3ad401f8959a\",6],\
 		[\"0xc6e9a76309f39b09\",1],[\"0xdd718d5cc53262d4\",1],[\"0xcbca25e39f142387\",2],\
 		[\"0xf78b278be53f454c\",2],[\"0xab3c0572291feb8b\",1],[\"0xbc9d89904f5b923f\",1]],\
 		\"transactionVersion\":1,\"stateVersion\":1}";
diff --git a/frame/bags-list/src/lib.rs b/frame/bags-list/src/lib.rs
index c502245409fdb..aa9f1c80dfdbc 100644
--- a/frame/bags-list/src/lib.rs
+++ b/frame/bags-list/src/lib.rs
@@ -70,7 +70,7 @@ pub mod mock;
 mod tests;
 pub mod weights;
 
-pub use list::{notional_bag_for, Bag, Error, List, Node};
+pub use list::{notional_bag_for, Bag, List, ListError, Node};
 pub use pallet::*;
 pub use weights::WeightInfo;
 
@@ -270,7 +270,7 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 }
 
 impl<T: Config<I>, I: 'static> SortedListProvider<T::AccountId> for Pallet<T, I> {
-	type Error = Error;
+	type Error = ListError;
 
 	type Score = T::Score;
 
@@ -286,7 +286,7 @@ impl<T: Config<I>, I: 'static> SortedListProvider<T::AccountId> for Pallet<T, I>
 		List::<T, I>::contains(id)
 	}
 
-	fn on_insert(id: T::AccountId, score: T::Score) -> Result<(), Error> {
+	fn on_insert(id: T::AccountId, score: T::Score) -> Result<(), ListError> {
 		List::<T, I>::insert(id, score)
 	}
 
diff --git a/frame/bags-list/src/list/mod.rs b/frame/bags-list/src/list/mod.rs
index 4921817c7e146..4e1287458bcb4 100644
--- a/frame/bags-list/src/list/mod.rs
+++ b/frame/bags-list/src/list/mod.rs
@@ -39,7 +39,7 @@ use sp_std::{
 };
 
 #[derive(Debug, PartialEq, Eq)]
-pub enum Error {
+pub enum ListError {
 	/// A duplicate id has been detected.
 	Duplicate,
 }
@@ -266,9 +266,9 @@ impl<T: Config<I>, I: 'static> List<T, I> {
 	/// Insert a new id into the appropriate bag in the list.
 	///
 	/// Returns an error if the list already contains `id`.
-	pub(crate) fn insert(id: T::AccountId, score: T::Score) -> Result<(), Error> {
+	pub(crate) fn insert(id: T::AccountId, score: T::Score) -> Result<(), ListError> {
 		if Self::contains(&id) {
-			return Err(Error::Duplicate)
+			return Err(ListError::Duplicate)
 		}
 
 		let bag_score = notional_bag_for::<T, I>(score);
diff --git a/frame/bags-list/src/list/tests.rs b/frame/bags-list/src/list/tests.rs
index 9b7a078b44284..c8e233f1e62cc 100644
--- a/frame/bags-list/src/list/tests.rs
+++ b/frame/bags-list/src/list/tests.rs
@@ -248,7 +248,7 @@ mod list {
 			// then
 			assert_storage_noop!(assert_eq!(
 				List::<Runtime>::insert(3, 20).unwrap_err(),
-				Error::Duplicate
+				ListError::Duplicate
 			));
 		});
 	}
diff --git a/frame/bags-list/src/tests.rs b/frame/bags-list/src/tests.rs
index 99396c9cbb3e3..0d6ba4721b9a2 100644
--- a/frame/bags-list/src/tests.rs
+++ b/frame/bags-list/src/tests.rs
@@ -518,7 +518,7 @@ mod sorted_list_provider {
 			// then
 			assert_storage_noop!(assert_eq!(
 				BagsList::on_insert(3, 20).unwrap_err(),
-				Error::Duplicate
+				ListError::Duplicate
 			));
 		});
 	}
diff --git a/frame/election-provider-multi-phase/src/lib.rs b/frame/election-provider-multi-phase/src/lib.rs
index b57d24d2d530c..ddc06ce0aecfd 100644
--- a/frame/election-provider-multi-phase/src/lib.rs
+++ b/frame/election-provider-multi-phase/src/lib.rs
@@ -1583,7 +1583,7 @@ impl<T: Config> ElectionProvider for Pallet<T> {
 /// number.
 pub fn dispatch_error_to_invalid(error: DispatchError) -> InvalidTransaction {
 	let error_number = match error {
-		DispatchError::Module(ModuleError { error, .. }) => error,
+		DispatchError::Module(ModuleError { error, .. }) => error[0],
 		_ => 0,
 	};
 	InvalidTransaction::Custom(error_number)
diff --git a/frame/election-provider-multi-phase/src/unsigned.rs b/frame/election-provider-multi-phase/src/unsigned.rs
index c52a4da22cb87..d210852bac19e 100644
--- a/frame/election-provider-multi-phase/src/unsigned.rs
+++ b/frame/election-provider-multi-phase/src/unsigned.rs
@@ -931,7 +931,7 @@ mod tests {
 	#[test]
 	#[should_panic(expected = "Invalid unsigned submission must produce invalid block and \
 	                           deprive validator from their authoring reward.: \
-	                           Module(ModuleError { index: 2, error: 1, message: \
+	                           Module(ModuleError { index: 2, error: [1, 0, 0, 0], message: \
 	                           Some(\"PreDispatchWrongWinnerCount\") })")]
 	fn unfeasible_solution_panics() {
 		ExtBuilder::default().build_and_execute(|| {
@@ -1053,7 +1053,7 @@ mod tests {
 				MultiPhase::basic_checks(&solution, "mined").unwrap_err(),
 				MinerError::PreDispatchChecksFailed(DispatchError::Module(ModuleError {
 					index: 2,
-					error: 1,
+					error: [1, 0, 0, 0],
 					message: Some("PreDispatchWrongWinnerCount"),
 				})),
 			);
diff --git a/frame/scheduler/src/mock.rs b/frame/scheduler/src/mock.rs
index 869425c2ff530..ecd04c3e48b52 100644
--- a/frame/scheduler/src/mock.rs
+++ b/frame/scheduler/src/mock.rs
@@ -38,7 +38,7 @@ use sp_runtime::{
 // Logger module to track execution.
 #[frame_support::pallet]
 pub mod logger {
-	use super::*;
+	use super::{OriginCaller, OriginTrait};
 	use frame_support::pallet_prelude::*;
 	use frame_system::pallet_prelude::*;
 	use std::cell::RefCell;
@@ -71,7 +71,7 @@ pub mod logger {
 	#[pallet::call]
 	impl<T: Config> Pallet<T>
 	where
-		<T as system::Config>::Origin: OriginTrait<PalletsOrigin = OriginCaller>,
+		<T as frame_system::Config>::Origin: OriginTrait<PalletsOrigin = OriginCaller>,
 	{
 		#[pallet::weight(*weight)]
 		pub fn log(origin: OriginFor<T>, i: u32, weight: Weight) -> DispatchResult {
diff --git a/frame/sudo/src/mock.rs b/frame/sudo/src/mock.rs
index 410807789069b..2e2a4abafcd98 100644
--- a/frame/sudo/src/mock.rs
+++ b/frame/sudo/src/mock.rs
@@ -34,7 +34,6 @@ use sp_runtime::{
 // Logger module to track execution.
 #[frame_support::pallet]
 pub mod logger {
-	use super::*;
 	use frame_support::pallet_prelude::*;
 	use frame_system::pallet_prelude::*;
 
diff --git a/frame/support/procedural/src/construct_runtime/mod.rs b/frame/support/procedural/src/construct_runtime/mod.rs
index 249eb072001c9..2a86869382c93 100644
--- a/frame/support/procedural/src/construct_runtime/mod.rs
+++ b/frame/support/procedural/src/construct_runtime/mod.rs
@@ -241,6 +241,7 @@ fn construct_runtime_final_expansion(
 		expand::expand_outer_inherent(&name, &block, &unchecked_extrinsic, &pallets, &scrate);
 	let validate_unsigned = expand::expand_outer_validate_unsigned(&name, &pallets, &scrate);
 	let integrity_test = decl_integrity_test(&scrate);
+	let static_assertions = decl_static_assertions(&name, &pallets, &scrate);
 
 	let res = quote!(
 		#scrate_decl
@@ -282,6 +283,8 @@ fn construct_runtime_final_expansion(
 		#validate_unsigned
 
 		#integrity_test
+
+		#static_assertions
 	);
 
 	Ok(res)
@@ -471,3 +474,34 @@ fn decl_integrity_test(scrate: &TokenStream2) -> TokenStream2 {
 		}
 	)
 }
+
+fn decl_static_assertions(
+	runtime: &Ident,
+	pallet_decls: &[Pallet],
+	scrate: &TokenStream2,
+) -> TokenStream2 {
+	let error_encoded_size_check = pallet_decls.iter().map(|decl| {
+		let path = &decl.path;
+		let assert_message = format!(
+			"The maximum encoded size of the error type in the `{}` pallet exceeds \
+			`MAX_MODULE_ERROR_ENCODED_SIZE`",
+			decl.name,
+		);
+
+		quote! {
+			#scrate::tt_call! {
+				macro = [{ #path::tt_error_token }]
+				frame_support = [{ #scrate }]
+				~~> #scrate::assert_error_encoded_size! {
+					path = [{ #path }]
+					runtime = [{ #runtime }]
+					assert_message = [{ #assert_message }]
+				}
+			}
+		}
+	});
+
+	quote! {
+		#(#error_encoded_size_check)*
+	}
+}
diff --git a/frame/support/procedural/src/lib.rs b/frame/support/procedural/src/lib.rs
index e2233fff72285..92564e94493c1 100644
--- a/frame/support/procedural/src/lib.rs
+++ b/frame/support/procedural/src/lib.rs
@@ -28,9 +28,11 @@ mod dummy_part_checker;
 mod key_prefix;
 mod match_and_insert;
 mod pallet;
+mod pallet_error;
 mod partial_eq_no_bound;
 mod storage;
 mod transactional;
+mod tt_macro;
 
 use proc_macro::TokenStream;
 use std::{cell::RefCell, str::FromStr};
@@ -41,9 +43,9 @@ thread_local! {
 	static COUNTER: RefCell<Counter> = RefCell::new(Counter(0));
 }
 
-/// Counter to generate a relatively unique identifier for macros querying for the existence of
-/// pallet parts. This is necessary because declarative macros gets hoisted to the crate root,
-/// which shares the namespace with other pallets containing the very same query macros.
+/// Counter to generate a relatively unique identifier for macros. This is necessary because
+/// declarative macros gets hoisted to the crate root, which shares the namespace with other pallets
+/// containing the very same macros.
 struct Counter(u64);
 
 impl Counter {
@@ -562,3 +564,14 @@ pub fn __generate_dummy_part_checker(input: TokenStream) -> TokenStream {
 pub fn match_and_insert(input: TokenStream) -> TokenStream {
 	match_and_insert::match_and_insert(input)
 }
+
+#[proc_macro_derive(PalletError, attributes(codec))]
+pub fn derive_pallet_error(input: TokenStream) -> TokenStream {
+	pallet_error::derive_pallet_error(input)
+}
+
+/// Internal macro used by `frame_support` to create tt-call-compliant macros
+#[proc_macro]
+pub fn __create_tt_macro(input: TokenStream) -> TokenStream {
+	tt_macro::create_tt_return_macro(input)
+}
diff --git a/frame/support/procedural/src/pallet/expand/error.rs b/frame/support/procedural/src/pallet/expand/error.rs
index 184fa86d3ae19..86b06d737decf 100644
--- a/frame/support/procedural/src/pallet/expand/error.rs
+++ b/frame/support/procedural/src/pallet/expand/error.rs
@@ -15,20 +15,48 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::pallet::Def;
+use crate::{
+	pallet::{parse::error::VariantField, Def},
+	COUNTER,
+};
 use frame_support_procedural_tools::get_doc_literals;
+use syn::spanned::Spanned;
 
 ///
 /// * impl various trait on Error
 pub fn expand_error(def: &mut Def) -> proc_macro2::TokenStream {
-	let error = if let Some(error) = &def.error { error } else { return Default::default() };
+	let count = COUNTER.with(|counter| counter.borrow_mut().inc());
+	let error_token_unique_id =
+		syn::Ident::new(&format!("__tt_error_token_{}", count), def.item.span());
 
-	let error_ident = &error.error;
 	let frame_support = &def.frame_support;
 	let frame_system = &def.frame_system;
+	let config_where_clause = &def.config.where_clause;
+
+	let error = if let Some(error) = &def.error {
+		error
+	} else {
+		return quote::quote! {
+			#[macro_export]
+			#[doc(hidden)]
+			macro_rules! #error_token_unique_id {
+				{
+					$caller:tt
+					frame_support = [{ $($frame_support:ident)::* }]
+				} => {
+					$($frame_support::)*tt_return! {
+						$caller
+					}
+				};
+			}
+
+			pub use #error_token_unique_id as tt_error_token;
+		}
+	};
+
+	let error_ident = &error.error;
 	let type_impl_gen = &def.type_impl_generics(error.attr_span);
 	let type_use_gen = &def.type_use_generics(error.attr_span);
-	let config_where_clause = &def.config.where_clause;
 
 	let phantom_variant: syn::Variant = syn::parse_quote!(
 		#[doc(hidden)]
@@ -39,13 +67,19 @@ pub fn expand_error(def: &mut Def) -> proc_macro2::TokenStream {
 		)
 	);
 
-	let as_u8_matches = error.variants.iter().enumerate().map(
-		|(i, (variant, _))| quote::quote_spanned!(error.attr_span => Self::#variant => #i as u8,),
-	);
-
-	let as_str_matches = error.variants.iter().map(|(variant, _)| {
-		let variant_str = format!("{}", variant);
-		quote::quote_spanned!(error.attr_span => Self::#variant => #variant_str,)
+	let as_str_matches = error.variants.iter().map(|(variant, field_ty, _)| {
+		let variant_str = variant.to_string();
+		match field_ty {
+			Some(VariantField { is_named: true }) => {
+				quote::quote_spanned!(error.attr_span => Self::#variant { .. } => #variant_str,)
+			},
+			Some(VariantField { is_named: false }) => {
+				quote::quote_spanned!(error.attr_span => Self::#variant(..) => #variant_str,)
+			},
+			None => {
+				quote::quote_spanned!(error.attr_span => Self::#variant => #variant_str,)
+			},
+		}
 	});
 
 	let error_item = {
@@ -62,9 +96,14 @@ pub fn expand_error(def: &mut Def) -> proc_macro2::TokenStream {
 	let capture_docs = if cfg!(feature = "no-metadata-docs") { "never" } else { "always" };
 
 	// derive TypeInfo for error metadata
-	error_item
-		.attrs
-		.push(syn::parse_quote!( #[derive(#frame_support::scale_info::TypeInfo)] ));
+	error_item.attrs.push(syn::parse_quote! {
+		#[derive(
+			#frame_support::codec::Encode,
+			#frame_support::codec::Decode,
+			#frame_support::scale_info::TypeInfo,
+			#frame_support::PalletError,
+		)]
+	});
 	error_item.attrs.push(syn::parse_quote!(
 		#[scale_info(skip_type_params(#type_use_gen), capture_docs = #capture_docs)]
 	));
@@ -90,14 +129,6 @@ pub fn expand_error(def: &mut Def) -> proc_macro2::TokenStream {
 		}
 
 		impl<#type_impl_gen> #error_ident<#type_use_gen> #config_where_clause {
-			#[doc(hidden)]
-			pub fn as_u8(&self) -> u8 {
-				match &self {
-					Self::__Ignore(_, _) => unreachable!("`__Ignore` can never be constructed"),
-					#( #as_u8_matches )*
-				}
-			}
-
 			#[doc(hidden)]
 			pub fn as_str(&self) -> &'static str {
 				match &self {
@@ -120,18 +151,37 @@ pub fn expand_error(def: &mut Def) -> proc_macro2::TokenStream {
 			#config_where_clause
 		{
 			fn from(err: #error_ident<#type_use_gen>) -> Self {
+				use #frame_support::codec::Encode;
 				let index = <
 					<T as #frame_system::Config>::PalletInfo
 					as #frame_support::traits::PalletInfo
 				>::index::<Pallet<#type_use_gen>>()
 					.expect("Every active module has an index in the runtime; qed") as u8;
+				let mut encoded = err.encode();
+				encoded.resize(#frame_support::MAX_MODULE_ERROR_ENCODED_SIZE, 0);
 
 				#frame_support::sp_runtime::DispatchError::Module(#frame_support::sp_runtime::ModuleError {
 					index,
-					error: err.as_u8(),
+					error: core::convert::TryInto::try_into(encoded).expect("encoded error is resized to be equal to the maximum encoded error size; qed"),
 					message: Some(err.as_str()),
 				})
 			}
 		}
+
+		#[macro_export]
+		#[doc(hidden)]
+		macro_rules! #error_token_unique_id {
+			{
+				$caller:tt
+				frame_support = [{ $($frame_support:ident)::* }]
+			} => {
+				$($frame_support::)*tt_return! {
+					$caller
+					error = [{ #error_ident }]
+				}
+			};
+		}
+
+		pub use #error_token_unique_id as tt_error_token;
 	)
 }
diff --git a/frame/support/procedural/src/pallet/parse/error.rs b/frame/support/procedural/src/pallet/parse/error.rs
index 419770386bf69..0ec49aa0adb49 100644
--- a/frame/support/procedural/src/pallet/parse/error.rs
+++ b/frame/support/procedural/src/pallet/parse/error.rs
@@ -18,20 +18,26 @@
 use super::helper;
 use frame_support_procedural_tools::get_doc_literals;
 use quote::ToTokens;
-use syn::spanned::Spanned;
+use syn::{spanned::Spanned, Fields};
 
 /// List of additional token to be used for parsing.
 mod keyword {
 	syn::custom_keyword!(Error);
 }
 
+/// Records information about the error enum variants.
+pub struct VariantField {
+	/// Whether or not the field is named, i.e. whether it is a tuple variant or struct variant.
+	pub is_named: bool,
+}
+
 /// This checks error declaration as a enum declaration with only variants without fields nor
 /// discriminant.
 pub struct ErrorDef {
 	/// The index of error item in pallet module.
 	pub index: usize,
-	/// Variants ident and doc literals (ordered as declaration order)
-	pub variants: Vec<(syn::Ident, Vec<syn::Lit>)>,
+	/// Variants ident, optional field and doc literals (ordered as declaration order)
+	pub variants: Vec<(syn::Ident, Option<VariantField>, Vec<syn::Lit>)>,
 	/// A set of usage of instance, must be check for consistency with trait.
 	pub instances: Vec<helper::InstanceUsage>,
 	/// The keyword error used (contains span).
@@ -70,18 +76,19 @@ impl ErrorDef {
 			.variants
 			.iter()
 			.map(|variant| {
-				if !matches!(variant.fields, syn::Fields::Unit) {
-					let msg = "Invalid pallet::error, unexpected fields, must be `Unit`";
-					return Err(syn::Error::new(variant.fields.span(), msg))
-				}
+				let field_ty = match &variant.fields {
+					Fields::Unit => None,
+					Fields::Named(_) => Some(VariantField { is_named: true }),
+					Fields::Unnamed(_) => Some(VariantField { is_named: false }),
+				};
 				if variant.discriminant.is_some() {
-					let msg = "Invalid pallet::error, unexpected discriminant, discriminant \
+					let msg = "Invalid pallet::error, unexpected discriminant, discriminants \
 						are not supported";
 					let span = variant.discriminant.as_ref().unwrap().0.span();
 					return Err(syn::Error::new(span, msg))
 				}
 
-				Ok((variant.ident.clone(), get_doc_literals(&variant.attrs)))
+				Ok((variant.ident.clone(), field_ty, get_doc_literals(&variant.attrs)))
 			})
 			.collect::<Result<_, _>>()?;
 
diff --git a/frame/support/procedural/src/pallet_error.rs b/frame/support/procedural/src/pallet_error.rs
new file mode 100644
index 0000000000000..216168131e43d
--- /dev/null
+++ b/frame/support/procedural/src/pallet_error.rs
@@ -0,0 +1,197 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2021 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use frame_support_procedural_tools::generate_crate_access_2018;
+use quote::ToTokens;
+use std::str::FromStr;
+
+// Derive `PalletError`
+pub fn derive_pallet_error(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+	let syn::DeriveInput { ident: name, generics, data, .. } = match syn::parse(input) {
+		Ok(input) => input,
+		Err(e) => return e.to_compile_error().into(),
+	};
+
+	let frame_support = match generate_crate_access_2018("frame-support") {
+		Ok(c) => c,
+		Err(e) => return e.into_compile_error().into(),
+	};
+	let frame_support = &frame_support;
+	let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+
+	let max_encoded_size = match data {
+		syn::Data::Struct(syn::DataStruct { fields, .. }) => match fields {
+			syn::Fields::Named(syn::FieldsNamed { named: fields, .. }) |
+			syn::Fields::Unnamed(syn::FieldsUnnamed { unnamed: fields, .. }) => {
+				let maybe_field_tys = fields
+					.iter()
+					.map(|f| generate_field_types(f, &frame_support))
+					.collect::<syn::Result<Vec<_>>>();
+				let field_tys = match maybe_field_tys {
+					Ok(tys) => tys.into_iter().flatten(),
+					Err(e) => return e.into_compile_error().into(),
+				};
+				quote::quote! {
+					0_usize
+					#(
+						.saturating_add(<
+							#field_tys as #frame_support::traits::PalletError
+						>::MAX_ENCODED_SIZE)
+					)*
+				}
+			},
+			syn::Fields::Unit => quote::quote!(0),
+		},
+		syn::Data::Enum(syn::DataEnum { variants, .. }) => {
+			let field_tys = variants
+				.iter()
+				.map(|variant| generate_variant_field_types(variant, &frame_support))
+				.collect::<Result<Vec<Option<Vec<proc_macro2::TokenStream>>>, syn::Error>>();
+
+			let field_tys = match field_tys {
+				Ok(tys) => tys.into_iter().flatten().collect::<Vec<_>>(),
+				Err(e) => return e.to_compile_error().into(),
+			};
+
+			// We start with `1`, because the discriminant of an enum is stored as u8
+			if field_tys.is_empty() {
+				quote::quote!(1)
+			} else {
+				let variant_sizes = field_tys.into_iter().map(|variant_field_tys| {
+					quote::quote! {
+						1_usize
+						#(.saturating_add(<
+							#variant_field_tys as #frame_support::traits::PalletError
+						>::MAX_ENCODED_SIZE))*
+					}
+				});
+
+				quote::quote! {{
+					let mut size = 1_usize;
+					let mut tmp = 0_usize;
+					#(
+						tmp = #variant_sizes;
+						size = if tmp > size { tmp } else { size };
+						tmp = 0_usize;
+					)*
+					size
+				}}
+			}
+		},
+		syn::Data::Union(syn::DataUnion { union_token, .. }) => {
+			let msg = "Cannot derive `PalletError` for union; please implement it directly";
+			return syn::Error::new(union_token.span, msg).into_compile_error().into()
+		},
+	};
+
+	quote::quote!(
+		const _: () = {
+			impl #impl_generics #frame_support::traits::PalletError
+				for #name #ty_generics #where_clause
+			{
+				const MAX_ENCODED_SIZE: usize = #max_encoded_size;
+			}
+		};
+	)
+	.into()
+}
+
+fn generate_field_types(
+	field: &syn::Field,
+	scrate: &syn::Ident,
+) -> syn::Result<Option<proc_macro2::TokenStream>> {
+	let attrs = &field.attrs;
+
+	for attr in attrs {
+		if attr.path.is_ident("codec") {
+			match attr.parse_meta()? {
+				syn::Meta::List(ref meta_list) if meta_list.nested.len() == 1 => {
+					match meta_list
+						.nested
+						.first()
+						.expect("Just checked that there is one item; qed")
+					{
+						syn::NestedMeta::Meta(syn::Meta::Path(path))
+							if path.get_ident().map_or(false, |i| i == "skip") =>
+							return Ok(None),
+
+						syn::NestedMeta::Meta(syn::Meta::Path(path))
+							if path.get_ident().map_or(false, |i| i == "compact") =>
+						{
+							let field_ty = &field.ty;
+							return Ok(Some(quote::quote!(#scrate::codec::Compact<#field_ty>)))
+						},
+
+						syn::NestedMeta::Meta(syn::Meta::NameValue(syn::MetaNameValue {
+							path,
+							lit: syn::Lit::Str(lit_str),
+							..
+						})) if path.get_ident().map_or(false, |i| i == "encoded_as") => {
+							let ty = proc_macro2::TokenStream::from_str(&lit_str.value())?;
+							return Ok(Some(ty))
+						},
+
+						_ => (),
+					}
+				},
+				_ => (),
+			}
+		}
+	}
+
+	Ok(Some(field.ty.to_token_stream()))
+}
+
+fn generate_variant_field_types(
+	variant: &syn::Variant,
+	scrate: &syn::Ident,
+) -> syn::Result<Option<Vec<proc_macro2::TokenStream>>> {
+	let attrs = &variant.attrs;
+
+	for attr in attrs {
+		if attr.path.is_ident("codec") {
+			match attr.parse_meta()? {
+				syn::Meta::List(ref meta_list) if meta_list.nested.len() == 1 => {
+					match meta_list
+						.nested
+						.first()
+						.expect("Just checked that there is one item; qed")
+					{
+						syn::NestedMeta::Meta(syn::Meta::Path(path))
+							if path.get_ident().map_or(false, |i| i == "skip") =>
+							return Ok(None),
+
+						_ => (),
+					}
+				},
+				_ => (),
+			}
+		}
+	}
+
+	match &variant.fields {
+		syn::Fields::Named(syn::FieldsNamed { named: fields, .. }) |
+		syn::Fields::Unnamed(syn::FieldsUnnamed { unnamed: fields, .. }) => {
+			let field_tys = fields
+				.iter()
+				.map(|field| generate_field_types(field, scrate))
+				.collect::<syn::Result<Vec<_>>>()?;
+			Ok(Some(field_tys.into_iter().flatten().collect()))
+		},
+		syn::Fields::Unit => Ok(None),
+	}
+}
diff --git a/frame/support/procedural/src/tt_macro.rs b/frame/support/procedural/src/tt_macro.rs
new file mode 100644
index 0000000000000..0a270a7173cfc
--- /dev/null
+++ b/frame/support/procedural/src/tt_macro.rs
@@ -0,0 +1,110 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2022 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Implementation of the `create_tt_return_macro` macro
+
+use crate::COUNTER;
+use frame_support_procedural_tools::generate_crate_access_2018;
+use proc_macro2::{Ident, TokenStream};
+use quote::format_ident;
+
+struct CreateTtReturnMacroDef {
+	name: Ident,
+	args: Vec<(Ident, TokenStream)>,
+}
+
+impl syn::parse::Parse for CreateTtReturnMacroDef {
+	fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+		let name = input.parse()?;
+		let _ = input.parse::<syn::Token![,]>()?;
+
+		let mut args = Vec::new();
+		while !input.is_empty() {
+			let mut value;
+			let key: Ident = input.parse()?;
+			let _ = input.parse::<syn::Token![=]>()?;
+			let _: syn::token::Bracket = syn::bracketed!(value in input);
+			let _: syn::token::Brace = syn::braced!(value in value);
+			let value: TokenStream = value.parse()?;
+
+			args.push((key, value))
+		}
+
+		Ok(Self { name, args })
+	}
+}
+
+/// A proc macro that accepts a name and any number of key-value pairs, to be used to create a
+/// declarative macro that follows tt-call conventions and simply calls [`tt_call::tt_return`],
+/// accepting an optional `frame-support` argument and returning the key-value pairs that were
+/// supplied to the proc macro.
+///
+/// # Example
+/// ```ignore
+/// __create_tt_macro! {
+///     my_tt_macro,
+///     foo = [{ bar }]
+/// }
+///
+/// // Creates the following declarative macro:
+///
+/// macro_rules! my_tt_macro {
+///     {
+///         $caller:tt
+///         $(frame_support = [{ $($frame_support:ident)::* }])?
+///     } => {
+///         frame_support::tt_return! {
+///             $caller
+///             foo = [{ bar }]
+///         }
+///     }
+/// }
+/// ```
+pub fn create_tt_return_macro(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+	let CreateTtReturnMacroDef { name, args } =
+		syn::parse_macro_input!(input as CreateTtReturnMacroDef);
+
+	let frame_support = match generate_crate_access_2018("frame-support") {
+		Ok(i) => i,
+		Err(e) => return e.into_compile_error().into(),
+	};
+	let (keys, values): (Vec<_>, Vec<_>) = args.into_iter().unzip();
+	let count = COUNTER.with(|counter| counter.borrow_mut().inc());
+	let unique_name = format_ident!("{}_{}", name, count);
+
+	let decl_macro = quote::quote! {
+		#[macro_export]
+		#[doc(hidden)]
+		macro_rules! #unique_name {
+			{
+				$caller:tt
+				$(frame_support = [{ $($frame_support:ident)::* }])?
+			} => {
+				#frame_support::tt_return! {
+					$caller
+					#(
+						#keys = [{ #values }]
+					)*
+				}
+			}
+		}
+
+		pub use #unique_name as #name;
+	};
+
+	decl_macro.into()
+}
diff --git a/frame/support/src/dispatch.rs b/frame/support/src/dispatch.rs
index ece5173f2f4ca..7ccf796167297 100644
--- a/frame/support/src/dispatch.rs
+++ b/frame/support/src/dispatch.rs
@@ -2003,6 +2003,10 @@ macro_rules! decl_module {
 		pub type Pallet<$trait_instance $(, $instance $( = $module_default_instance)?)?>
 			= $mod_type<$trait_instance $(, $instance)?>;
 
+		$crate::__create_tt_macro! {
+			tt_error_token,
+		}
+
 		$crate::decl_module! {
 			@impl_on_initialize
 			{ $system }
diff --git a/frame/support/src/error.rs b/frame/support/src/error.rs
index 4880bba5c5e97..764376a4e1dc2 100644
--- a/frame/support/src/error.rs
+++ b/frame/support/src/error.rs
@@ -85,7 +85,12 @@ macro_rules! decl_error {
 		}
 	) => {
 		$(#[$attr])*
-		#[derive($crate::scale_info::TypeInfo)]
+		#[derive(
+			$crate::codec::Encode,
+			$crate::codec::Decode,
+			$crate::scale_info::TypeInfo,
+			$crate::PalletError,
+		)]
 		#[scale_info(skip_type_params($generic $(, $inst_generic)?), capture_docs = "always")]
 		pub enum $error<$generic: $trait $(, $inst_generic: $instance)?>
 		$( where $( $where_ty: $where_bound ),* )?
@@ -114,17 +119,6 @@ macro_rules! decl_error {
 		impl<$generic: $trait $(, $inst_generic: $instance)?> $error<$generic $(, $inst_generic)?>
 		$( where $( $where_ty: $where_bound ),* )?
 		{
-			fn as_u8(&self) -> u8 {
-				$crate::decl_error! {
-					@GENERATE_AS_U8
-					self
-					$error
-					{}
-					0,
-					$( $name ),*
-				}
-			}
-
 			fn as_str(&self) -> &'static str {
 				match self {
 					Self::__Ignore(_, _) => unreachable!("`__Ignore` can never be constructed"),
@@ -149,47 +143,19 @@ macro_rules! decl_error {
 		$( where $( $where_ty: $where_bound ),* )?
 		{
 			fn from(err: $error<$generic $(, $inst_generic)?>) -> Self {
+				use $crate::codec::Encode;
 				let index = <$generic::PalletInfo as $crate::traits::PalletInfo>
 					::index::<$module<$generic $(, $inst_generic)?>>()
 					.expect("Every active module has an index in the runtime; qed") as u8;
+				let mut error = err.encode();
+				error.resize($crate::MAX_MODULE_ERROR_ENCODED_SIZE, 0);
 
 				$crate::sp_runtime::DispatchError::Module($crate::sp_runtime::ModuleError {
 					index,
-					error: err.as_u8(),
+					error: core::convert::TryInto::try_into(error).expect("encoded error is resized to be equal to the maximum encoded error size; qed"),
 					message: Some(err.as_str()),
 				})
 			}
 		}
 	};
-	(@GENERATE_AS_U8
-		$self:ident
-		$error:ident
-		{ $( $generated:tt )* }
-		$index:expr,
-		$name:ident
-		$( , $rest:ident )*
-	) => {
-		$crate::decl_error! {
-			@GENERATE_AS_U8
-			$self
-			$error
-			{
-				$( $generated )*
-				$error::$name => $index,
-			}
-			$index + 1,
-			$( $rest ),*
-		}
-	};
-	(@GENERATE_AS_U8
-		$self:ident
-		$error:ident
-		{ $( $generated:tt )* }
-		$index:expr,
-	) => {
-		match $self {
-			$error::__Ignore(_, _) => unreachable!("`__Ignore` can never be constructed"),
-			$( $generated )*
-		}
-	}
 }
diff --git a/frame/support/src/lib.rs b/frame/support/src/lib.rs
index 3988b5e9af219..f290b3ed9d533 100644
--- a/frame/support/src/lib.rs
+++ b/frame/support/src/lib.rs
@@ -93,7 +93,9 @@ pub use self::{
 		StorageMap, StorageNMap, StoragePrefixedMap, StorageValue,
 	},
 };
-pub use sp_runtime::{self, print, traits::Printable, ConsensusEngineId};
+pub use sp_runtime::{
+	self, print, traits::Printable, ConsensusEngineId, MAX_MODULE_ERROR_ENCODED_SIZE,
+};
 
 use codec::{Decode, Encode};
 use scale_info::TypeInfo;
@@ -103,7 +105,7 @@ use sp_runtime::TypeId;
 pub const LOG_TARGET: &'static str = "runtime::frame-support";
 
 /// A type that cannot be instantiated.
-#[derive(Debug, PartialEq, Eq, Clone, TypeInfo)]
+#[derive(Encode, Decode, Debug, PartialEq, Eq, Clone, TypeInfo)]
 pub enum Never {}
 
 /// A pallet identifier. These are per pallet and should be stored in a registry somewhere.
@@ -598,11 +600,12 @@ pub fn debug(data: &impl sp_std::fmt::Debug) {
 
 #[doc(inline)]
 pub use frame_support_procedural::{
-	construct_runtime, decl_storage, match_and_insert, transactional, RuntimeDebugNoBound,
+	construct_runtime, decl_storage, match_and_insert, transactional, PalletError,
+	RuntimeDebugNoBound,
 };
 
 #[doc(hidden)]
-pub use frame_support_procedural::__generate_dummy_part_checker;
+pub use frame_support_procedural::{__create_tt_macro, __generate_dummy_part_checker};
 
 /// Derive [`Clone`] but do not bound any generic.
 ///
@@ -847,6 +850,32 @@ macro_rules! assert_ok {
 	};
 }
 
+/// Assert that the maximum encoding size does not exceed the value defined in
+/// [`MAX_MODULE_ERROR_ENCODED_SIZE`] during compilation.
+///
+/// This macro is intended to be used in conjunction with `tt_call!`.
+#[macro_export]
+macro_rules! assert_error_encoded_size {
+	{
+		path = [{ $($path:ident)::+ }]
+		runtime = [{ $runtime:ident }]
+		assert_message = [{ $assert_message:literal }]
+		error = [{ $error:ident }]
+	} => {
+		const _: () = assert!(
+			<
+				$($path::)+$error<$runtime> as $crate::traits::PalletError
+			>::MAX_ENCODED_SIZE <= $crate::MAX_MODULE_ERROR_ENCODED_SIZE,
+			$assert_message
+		);
+	};
+	{
+		path = [{ $($path:ident)::+ }]
+		runtime = [{ $runtime:ident }]
+		assert_message = [{ $assert_message:literal }]
+	} => {};
+}
+
 #[cfg(feature = "std")]
 #[doc(hidden)]
 pub use serde::{Deserialize, Serialize};
@@ -1361,6 +1390,7 @@ pub mod pallet_prelude {
 			TransactionTag, TransactionValidity, TransactionValidityError, UnknownTransaction,
 			ValidTransaction,
 		},
+		MAX_MODULE_ERROR_ENCODED_SIZE,
 	};
 	pub use sp_std::marker::PhantomData;
 }
@@ -1638,10 +1668,25 @@ pub mod pallet_prelude {
 /// pub enum Error<T> {
 /// 	/// $some_optional_doc
 /// 	$SomeFieldLessVariant,
+/// 	/// $some_more_optional_doc
+/// 	$SomeVariantWithOneField(FieldType),
 /// 	...
 /// }
 /// ```
-/// I.e. a regular rust enum named `Error`, with generic `T` and fieldless variants.
+/// I.e. a regular rust enum named `Error`, with generic `T` and fieldless or multiple-field
+/// variants.
+///
+/// Any field type in the enum variants must implement [`scale_info::TypeInfo`] in order to be
+/// properly used in the metadata, and its encoded size should be as small as possible,
+/// preferably 1 byte in size in order to reduce storage size. The error enum itself has an
+/// absolute maximum encoded size specified by [`MAX_MODULE_ERROR_ENCODED_SIZE`].
+///
+/// Field types in enum variants must also implement [`PalletError`](traits::PalletError),
+/// otherwise the pallet will fail to compile. Rust primitive types have already implemented
+/// the [`PalletError`](traits::PalletError) trait along with some commonly used stdlib types
+/// such as `Option` and `PhantomData`, and hence in most use cases, a manual implementation is
+/// not necessary and is discouraged.
+///
 /// The generic `T` mustn't bound anything and where clause is not allowed. But bounds and
 /// where clause shouldn't be needed for any usecase.
 ///
diff --git a/frame/support/src/traits.rs b/frame/support/src/traits.rs
index a8ce78ae9dabc..40afc0d337f43 100644
--- a/frame/support/src/traits.rs
+++ b/frame/support/src/traits.rs
@@ -46,6 +46,9 @@ pub use validation::{
 	ValidatorSetWithIdentification, VerifySeal,
 };
 
+mod error;
+pub use error::PalletError;
+
 mod filter;
 pub use filter::{ClearFilterGuard, FilterStack, FilterStackGuard, InstanceFilter, IntegrityTest};
 
diff --git a/frame/support/src/traits/error.rs b/frame/support/src/traits/error.rs
new file mode 100644
index 0000000000000..8e26891669e65
--- /dev/null
+++ b/frame/support/src/traits/error.rs
@@ -0,0 +1,95 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2022 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Traits for describing and constraining pallet error types.
+use codec::{Compact, Decode, Encode};
+use sp_std::marker::PhantomData;
+
+/// Trait indicating that the implementing type is going to be included as a field in a variant of
+/// the `#[pallet::error]` enum type.
+///
+/// ## Notes
+///
+/// The pallet error enum has a maximum encoded size as defined by
+/// [`frame_support::MAX_MODULE_ERROR_ENCODED_SIZE`]. If the pallet error type exceeds this size
+/// limit, a static assertion during compilation will fail. The compilation error will be in the
+/// format of `error[E0080]: evaluation of constant value failed` due to the usage of
+/// const assertions.
+pub trait PalletError: Encode + Decode {
+	/// The maximum encoded size for the implementing type.
+	///
+	/// This will be used to check whether the pallet error type is less than or equal to
+	/// [`frame_support::MAX_MODULE_ERROR_ENCODED_SIZE`], and if it is, a compilation error will be
+	/// thrown.
+	const MAX_ENCODED_SIZE: usize;
+}
+
+macro_rules! impl_for_types {
+	(size: $size:expr, $($typ:ty),+) => {
+		$(
+			impl PalletError for $typ {
+				const MAX_ENCODED_SIZE: usize = $size;
+			}
+		)+
+	};
+}
+
+impl_for_types!(size: 0, (), crate::Never);
+impl_for_types!(size: 1, u8, i8, bool);
+impl_for_types!(size: 2, u16, i16, Compact<u8>);
+impl_for_types!(size: 4, u32, i32, Compact<u16>);
+impl_for_types!(size: 5, Compact<u32>);
+impl_for_types!(size: 8, u64, i64);
+impl_for_types!(size: 9, Compact<u64>);
+// Contains a u64 for secs and u32 for nanos, hence 12 bytes
+impl_for_types!(size: 12, core::time::Duration);
+impl_for_types!(size: 16, u128, i128);
+impl_for_types!(size: 17, Compact<u128>);
+
+impl<T> PalletError for PhantomData<T> {
+	const MAX_ENCODED_SIZE: usize = 0;
+}
+
+impl<T: PalletError> PalletError for core::ops::Range<T> {
+	const MAX_ENCODED_SIZE: usize = T::MAX_ENCODED_SIZE.saturating_mul(2);
+}
+
+impl<T: PalletError, const N: usize> PalletError for [T; N] {
+	const MAX_ENCODED_SIZE: usize = T::MAX_ENCODED_SIZE.saturating_mul(N);
+}
+
+impl<T: PalletError> PalletError for Option<T> {
+	const MAX_ENCODED_SIZE: usize = T::MAX_ENCODED_SIZE.saturating_add(1);
+}
+
+impl<T: PalletError, E: PalletError> PalletError for Result<T, E> {
+	const MAX_ENCODED_SIZE: usize = if T::MAX_ENCODED_SIZE > E::MAX_ENCODED_SIZE {
+		T::MAX_ENCODED_SIZE
+	} else {
+		E::MAX_ENCODED_SIZE
+	}
+	.saturating_add(1);
+}
+
+#[impl_trait_for_tuples::impl_for_tuples(1, 18)]
+impl PalletError for Tuple {
+	const MAX_ENCODED_SIZE: usize = {
+		let mut size = 0_usize;
+		for_tuples!( #(size = size.saturating_add(Tuple::MAX_ENCODED_SIZE);)* );
+		size
+	};
+}
diff --git a/frame/support/test/tests/construct_runtime.rs b/frame/support/test/tests/construct_runtime.rs
index b3f8feb8aa4b2..804deb08919a4 100644
--- a/frame/support/test/tests/construct_runtime.rs
+++ b/frame/support/test/tests/construct_runtime.rs
@@ -271,139 +271,95 @@ pub type Header = generic::Header<BlockNumber, BlakeTwo256>;
 pub type Block = generic::Block<Header, UncheckedExtrinsic>;
 pub type UncheckedExtrinsic = generic::UncheckedExtrinsic<u32, Call, Signature, ()>;
 
-mod origin_test {
-	use super::{module3, nested, system, Block, UncheckedExtrinsic};
-	use frame_support::traits::{Contains, OriginTrait};
-
-	impl nested::module3::Config for RuntimeOriginTest {}
-	impl module3::Config for RuntimeOriginTest {}
-
-	pub struct BaseCallFilter;
-	impl Contains<Call> for BaseCallFilter {
-		fn contains(c: &Call) -> bool {
-			match c {
-				Call::NestedModule3(_) => true,
-				_ => false,
-			}
-		}
-	}
-
-	impl system::Config for RuntimeOriginTest {
-		type BaseCallFilter = BaseCallFilter;
-		type Hash = super::H256;
-		type Origin = Origin;
-		type BlockNumber = super::BlockNumber;
-		type AccountId = u32;
-		type Event = Event;
-		type PalletInfo = PalletInfo;
-		type Call = Call;
-		type DbWeight = ();
-	}
-
-	frame_support::construct_runtime!(
-		pub enum RuntimeOriginTest where
-			Block = Block,
-			NodeBlock = Block,
-			UncheckedExtrinsic = UncheckedExtrinsic
-		{
-			System: system::{Pallet, Event<T>, Origin<T>},
-			NestedModule3: nested::module3::{Pallet, Origin, Call},
-			Module3: module3::{Pallet, Origin<T>, Call},
-		}
-	);
-
-	#[test]
-	fn origin_default_filter() {
-		let accepted_call = nested::module3::Call::fail {}.into();
-		let rejected_call = module3::Call::fail {}.into();
-
-		assert_eq!(Origin::root().filter_call(&accepted_call), true);
-		assert_eq!(Origin::root().filter_call(&rejected_call), true);
-		assert_eq!(Origin::none().filter_call(&accepted_call), true);
-		assert_eq!(Origin::none().filter_call(&rejected_call), false);
-		assert_eq!(Origin::signed(0).filter_call(&accepted_call), true);
-		assert_eq!(Origin::signed(0).filter_call(&rejected_call), false);
-		assert_eq!(Origin::from(Some(0)).filter_call(&accepted_call), true);
-		assert_eq!(Origin::from(Some(0)).filter_call(&rejected_call), false);
-		assert_eq!(Origin::from(None).filter_call(&accepted_call), true);
-		assert_eq!(Origin::from(None).filter_call(&rejected_call), false);
-		assert_eq!(Origin::from(super::nested::module3::Origin).filter_call(&accepted_call), true);
-		assert_eq!(Origin::from(super::nested::module3::Origin).filter_call(&rejected_call), false);
-
-		let mut origin = Origin::from(Some(0));
-		origin.add_filter(|c| matches!(c, Call::Module3(_)));
-		assert_eq!(origin.filter_call(&accepted_call), false);
-		assert_eq!(origin.filter_call(&rejected_call), false);
-
-		// Now test for root origin and filters:
-		let mut origin = Origin::from(Some(0));
-		origin.set_caller_from(Origin::root());
-		assert!(matches!(origin.caller, OriginCaller::system(super::system::RawOrigin::Root)));
-
-		// Root origin bypass all filter.
-		assert_eq!(origin.filter_call(&accepted_call), true);
-		assert_eq!(origin.filter_call(&rejected_call), true);
-
-		origin.set_caller_from(Origin::from(Some(0)));
-
-		// Back to another signed origin, the filtered are now effective again
-		assert_eq!(origin.filter_call(&accepted_call), true);
-		assert_eq!(origin.filter_call(&rejected_call), false);
-
-		origin.set_caller_from(Origin::root());
-		origin.reset_filter();
-
-		// Root origin bypass all filter, even when they are reset.
-		assert_eq!(origin.filter_call(&accepted_call), true);
-		assert_eq!(origin.filter_call(&rejected_call), true);
-	}
-}
-
 #[test]
 fn check_modules_error_type() {
 	assert_eq!(
 		Module1_1::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 31, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 31,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module2::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 32, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 32,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module1_2::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 33, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 33,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		NestedModule3::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 34, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 34,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module1_3::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 6, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 6,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module1_4::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 3, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 3,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module1_5::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 4, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 4,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module1_6::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 1, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 1,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module1_7::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 2, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 2,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module1_8::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 12, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 12,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 	assert_eq!(
 		Module1_9::fail(system::Origin::<Runtime>::Root.into()),
-		Err(DispatchError::Module(ModuleError { index: 13, error: 0, message: Some("Something") })),
+		Err(DispatchError::Module(ModuleError {
+			index: 13,
+			error: [0; 4],
+			message: Some("Something")
+		})),
 	);
 }
 
diff --git a/frame/support/test/tests/construct_runtime_ui/pallet_error_too_large.rs b/frame/support/test/tests/construct_runtime_ui/pallet_error_too_large.rs
new file mode 100644
index 0000000000000..827d8a58af733
--- /dev/null
+++ b/frame/support/test/tests/construct_runtime_ui/pallet_error_too_large.rs
@@ -0,0 +1,85 @@
+use frame_support::construct_runtime;
+use sp_runtime::{generic, traits::BlakeTwo256};
+use sp_core::sr25519;
+
+#[frame_support::pallet]
+mod pallet {
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+	#[pallet::error]
+	pub enum Error<T> {
+		MyError(crate::Nested1),
+	}
+}
+
+#[derive(scale_info::TypeInfo, frame_support::PalletError, codec::Encode, codec::Decode)]
+pub enum Nested1 {
+	Nested2(Nested2)
+}
+
+#[derive(scale_info::TypeInfo, frame_support::PalletError, codec::Encode, codec::Decode)]
+pub enum Nested2 {
+	Nested3(Nested3)
+}
+
+#[derive(scale_info::TypeInfo, frame_support::PalletError, codec::Encode, codec::Decode)]
+pub enum Nested3 {
+	Nested4(Nested4)
+}
+
+#[derive(scale_info::TypeInfo, frame_support::PalletError, codec::Encode, codec::Decode)]
+pub enum Nested4 {
+	Num(u8)
+}
+
+pub type Signature = sr25519::Signature;
+pub type BlockNumber = u32;
+pub type Header = generic::Header<BlockNumber, BlakeTwo256>;
+pub type Block = generic::Block<Header, UncheckedExtrinsic>;
+pub type UncheckedExtrinsic = generic::UncheckedExtrinsic<u32, Call, Signature, ()>;
+
+impl pallet::Config for Runtime {}
+
+impl frame_system::Config for Runtime {
+	type BaseCallFilter = frame_support::traits::Everything;
+	type Origin = Origin;
+	type Index = u64;
+	type BlockNumber = u32;
+	type Call = Call;
+	type Hash = sp_runtime::testing::H256;
+	type Hashing = sp_runtime::traits::BlakeTwo256;
+	type AccountId = u64;
+	type Lookup = sp_runtime::traits::IdentityLookup<Self::AccountId>;
+	type Header = Header;
+	type Event = Event;
+	type BlockHashCount = frame_support::traits::ConstU32<250>;
+	type BlockWeights = ();
+	type BlockLength = ();
+	type DbWeight = ();
+	type Version = ();
+	type PalletInfo = PalletInfo;
+	type AccountData = ();
+	type OnNewAccount = ();
+	type OnKilledAccount = ();
+	type SystemWeightInfo = ();
+	type SS58Prefix = ();
+	type OnSetCode = ();
+	type MaxConsumers = frame_support::traits::ConstU32<16>;
+}
+
+construct_runtime! {
+	pub enum Runtime where
+		Block = Block,
+		NodeBlock = Block,
+		UncheckedExtrinsic = UncheckedExtrinsic
+	{
+		System: frame_system::{Pallet, Call, Storage, Config, Event<T>},
+		Pallet: pallet::{Pallet},
+	}
+}
+
+fn main() {}
diff --git a/frame/support/test/tests/construct_runtime_ui/pallet_error_too_large.stderr b/frame/support/test/tests/construct_runtime_ui/pallet_error_too_large.stderr
new file mode 100644
index 0000000000000..161873866b6f3
--- /dev/null
+++ b/frame/support/test/tests/construct_runtime_ui/pallet_error_too_large.stderr
@@ -0,0 +1,13 @@
+error[E0080]: evaluation of constant value failed
+  --> tests/construct_runtime_ui/pallet_error_too_large.rs:74:1
+   |
+74 | / construct_runtime! {
+75 | |     pub enum Runtime where
+76 | |         Block = Block,
+77 | |         NodeBlock = Block,
+...  |
+82 | |     }
+83 | | }
+   | |_^ the evaluated program panicked at 'The maximum encoded size of the error type in the `Pallet` pallet exceeds `MAX_MODULE_ERROR_ENCODED_SIZE`', $DIR/tests/construct_runtime_ui/pallet_error_too_large.rs:74:1
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2021` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/frame/support/test/tests/origin.rs b/frame/support/test/tests/origin.rs
new file mode 100644
index 0000000000000..1def44c15b48f
--- /dev/null
+++ b/frame/support/test/tests/origin.rs
@@ -0,0 +1,214 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2021 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Origin tests for construct_runtime macro
+
+#![recursion_limit = "128"]
+
+use frame_support::traits::{Contains, OriginTrait};
+use scale_info::TypeInfo;
+use sp_core::{sr25519, H256};
+use sp_runtime::{generic, traits::BlakeTwo256};
+
+mod system;
+
+mod nested {
+	use super::*;
+
+	pub mod module {
+		use super::*;
+
+		pub trait Config: system::Config {}
+
+		frame_support::decl_module! {
+			pub struct Module<T: Config> for enum Call
+				where origin: <T as system::Config>::Origin, system=system
+			{
+				#[weight = 0]
+				pub fn fail(_origin) -> frame_support::dispatch::DispatchResult {
+					Err(Error::<T>::Something.into())
+				}
+			}
+		}
+
+		#[derive(Clone, PartialEq, Eq, Debug, codec::Encode, codec::Decode, TypeInfo)]
+		pub struct Origin;
+
+		frame_support::decl_event! {
+			pub enum Event {
+				A,
+			}
+		}
+
+		frame_support::decl_error! {
+			pub enum Error for Module<T: Config> {
+				Something
+			}
+		}
+
+		frame_support::decl_storage! {
+			trait Store for Module<T: Config> as Module {}
+			add_extra_genesis {
+				build(|_config| {})
+			}
+		}
+	}
+}
+
+pub mod module {
+	use super::*;
+
+	pub trait Config: system::Config {}
+
+	frame_support::decl_module! {
+		pub struct Module<T: Config> for enum Call
+			where origin: <T as system::Config>::Origin, system=system
+		{
+			#[weight = 0]
+			pub fn fail(_origin) -> frame_support::dispatch::DispatchResult {
+				Err(Error::<T>::Something.into())
+			}
+			#[weight = 0]
+			pub fn aux_1(_origin, #[compact] _data: u32) -> frame_support::dispatch::DispatchResult {
+				unreachable!()
+			}
+			#[weight = 0]
+			pub fn aux_2(_origin, _data: i32, #[compact] _data2: u32) -> frame_support::dispatch::DispatchResult {
+				unreachable!()
+			}
+			#[weight = 0]
+			fn aux_3(_origin, _data: i32, _data2: String) -> frame_support::dispatch::DispatchResult {
+				unreachable!()
+			}
+			#[weight = 3]
+			fn aux_4(_origin) -> frame_support::dispatch::DispatchResult { unreachable!() }
+			#[weight = (5, frame_support::weights::DispatchClass::Operational)]
+			fn operational(_origin) { unreachable!() }
+		}
+	}
+
+	#[derive(Clone, PartialEq, Eq, Debug, codec::Encode, codec::Decode, TypeInfo)]
+	pub struct Origin<T>(pub core::marker::PhantomData<T>);
+
+	frame_support::decl_event! {
+		pub enum Event {
+			A,
+		}
+	}
+
+	frame_support::decl_error! {
+		pub enum Error for Module<T: Config> {
+			Something
+		}
+	}
+
+	frame_support::decl_storage! {
+		trait Store for Module<T: Config> as Module {}
+		add_extra_genesis {
+			build(|_config| {})
+		}
+	}
+}
+
+impl nested::module::Config for RuntimeOriginTest {}
+impl module::Config for RuntimeOriginTest {}
+
+pub struct BaseCallFilter;
+impl Contains<Call> for BaseCallFilter {
+	fn contains(c: &Call) -> bool {
+		match c {
+			Call::NestedModule(_) => true,
+			_ => false,
+		}
+	}
+}
+
+impl system::Config for RuntimeOriginTest {
+	type BaseCallFilter = BaseCallFilter;
+	type Hash = H256;
+	type Origin = Origin;
+	type BlockNumber = BlockNumber;
+	type AccountId = u32;
+	type Event = Event;
+	type PalletInfo = PalletInfo;
+	type Call = Call;
+	type DbWeight = ();
+}
+
+frame_support::construct_runtime!(
+	pub enum RuntimeOriginTest where
+		Block = Block,
+		NodeBlock = Block,
+		UncheckedExtrinsic = UncheckedExtrinsic
+	{
+		System: system::{Pallet, Event<T>, Origin<T>},
+		NestedModule: nested::module::{Pallet, Origin, Call},
+		Module: module::{Pallet, Origin<T>, Call},
+	}
+);
+
+pub type Signature = sr25519::Signature;
+pub type BlockNumber = u64;
+pub type Header = generic::Header<BlockNumber, BlakeTwo256>;
+pub type UncheckedExtrinsic = generic::UncheckedExtrinsic<u32, Call, Signature, ()>;
+pub type Block = generic::Block<Header, UncheckedExtrinsic>;
+
+#[test]
+fn origin_default_filter() {
+	let accepted_call = nested::module::Call::fail {}.into();
+	let rejected_call = module::Call::fail {}.into();
+
+	assert_eq!(Origin::root().filter_call(&accepted_call), true);
+	assert_eq!(Origin::root().filter_call(&rejected_call), true);
+	assert_eq!(Origin::none().filter_call(&accepted_call), true);
+	assert_eq!(Origin::none().filter_call(&rejected_call), false);
+	assert_eq!(Origin::signed(0).filter_call(&accepted_call), true);
+	assert_eq!(Origin::signed(0).filter_call(&rejected_call), false);
+	assert_eq!(Origin::from(Some(0)).filter_call(&accepted_call), true);
+	assert_eq!(Origin::from(Some(0)).filter_call(&rejected_call), false);
+	assert_eq!(Origin::from(None).filter_call(&accepted_call), true);
+	assert_eq!(Origin::from(None).filter_call(&rejected_call), false);
+	assert_eq!(Origin::from(nested::module::Origin).filter_call(&accepted_call), true);
+	assert_eq!(Origin::from(nested::module::Origin).filter_call(&rejected_call), false);
+
+	let mut origin = Origin::from(Some(0));
+	origin.add_filter(|c| matches!(c, Call::Module(_)));
+	assert_eq!(origin.filter_call(&accepted_call), false);
+	assert_eq!(origin.filter_call(&rejected_call), false);
+
+	// Now test for root origin and filters:
+	let mut origin = Origin::from(Some(0));
+	origin.set_caller_from(Origin::root());
+	assert!(matches!(origin.caller, OriginCaller::system(system::RawOrigin::Root)));
+
+	// Root origin bypass all filter.
+	assert_eq!(origin.filter_call(&accepted_call), true);
+	assert_eq!(origin.filter_call(&rejected_call), true);
+
+	origin.set_caller_from(Origin::from(Some(0)));
+
+	// Back to another signed origin, the filtered are now effective again
+	assert_eq!(origin.filter_call(&accepted_call), true);
+	assert_eq!(origin.filter_call(&rejected_call), false);
+
+	origin.set_caller_from(Origin::root());
+	origin.reset_filter();
+
+	// Root origin bypass all filter, even when they are reset.
+	assert_eq!(origin.filter_call(&accepted_call), true);
+	assert_eq!(origin.filter_call(&rejected_call), true);
+}
diff --git a/frame/support/test/tests/pallet.rs b/frame/support/test/tests/pallet.rs
index 451cb2e7b889e..83f6a722f93aa 100644
--- a/frame/support/test/tests/pallet.rs
+++ b/frame/support/test/tests/pallet.rs
@@ -20,7 +20,7 @@ use frame_support::{
 	storage::unhashed,
 	traits::{
 		ConstU32, GetCallName, GetStorageVersion, OnFinalize, OnGenesis, OnInitialize,
-		OnRuntimeUpgrade, PalletInfoAccess, StorageVersion,
+		OnRuntimeUpgrade, PalletError, PalletInfoAccess, StorageVersion,
 	},
 	weights::{DispatchClass, DispatchInfo, GetDispatchInfo, Pays, RuntimeDbWeight},
 };
@@ -229,9 +229,14 @@ pub mod pallet {
 	}
 
 	#[pallet::error]
+	#[derive(PartialEq, Eq)]
 	pub enum Error<T> {
 		/// doc comment put into metadata
 		InsufficientProposersBalance,
+		Code(u8),
+		#[codec(skip)]
+		Skipped(u128),
+		CompactU8(#[codec(compact)] u8),
 	}
 
 	#[pallet::event]
@@ -656,10 +661,11 @@ fn error_expand() {
 		DispatchError::from(pallet::Error::<Runtime>::InsufficientProposersBalance),
 		DispatchError::Module(ModuleError {
 			index: 1,
-			error: 0,
+			error: [0, 0, 0, 0],
 			message: Some("InsufficientProposersBalance")
 		}),
 	);
+	assert_eq!(<pallet::Error::<Runtime> as PalletError>::MAX_ENCODED_SIZE, 3);
 }
 
 #[test]
diff --git a/frame/support/test/tests/pallet_instance.rs b/frame/support/test/tests/pallet_instance.rs
index 30b9bcda88d1e..118794e2fa20a 100644
--- a/frame/support/test/tests/pallet_instance.rs
+++ b/frame/support/test/tests/pallet_instance.rs
@@ -343,7 +343,7 @@ fn error_expand() {
 		DispatchError::from(pallet::Error::<Runtime>::InsufficientProposersBalance),
 		DispatchError::Module(ModuleError {
 			index: 1,
-			error: 0,
+			error: [0; 4],
 			message: Some("InsufficientProposersBalance")
 		}),
 	);
@@ -364,7 +364,7 @@ fn error_expand() {
 		),
 		DispatchError::Module(ModuleError {
 			index: 2,
-			error: 0,
+			error: [0; 4],
 			message: Some("InsufficientProposersBalance")
 		}),
 	);
diff --git a/frame/support/test/tests/pallet_ui/error_no_fieldless.rs b/frame/support/test/tests/pallet_ui/error_does_not_derive_pallet_error.rs
similarity index 50%
rename from frame/support/test/tests/pallet_ui/error_no_fieldless.rs
rename to frame/support/test/tests/pallet_ui/error_does_not_derive_pallet_error.rs
index c9d444d6f90dd..254d65866774f 100644
--- a/frame/support/test/tests/pallet_ui/error_no_fieldless.rs
+++ b/frame/support/test/tests/pallet_ui/error_does_not_derive_pallet_error.rs
@@ -1,25 +1,19 @@
 #[frame_support::pallet]
 mod pallet {
-	use frame_support::pallet_prelude::Hooks;
-	use frame_system::pallet_prelude::BlockNumberFor;
-
 	#[pallet::config]
 	pub trait Config: frame_system::Config {}
 
 	#[pallet::pallet]
 	pub struct Pallet<T>(core::marker::PhantomData<T>);
 
-	#[pallet::hooks]
-	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {}
-
-	#[pallet::call]
-	impl<T: Config> Pallet<T> {}
-
 	#[pallet::error]
 	pub enum Error<T> {
-		U8(u8),
+		CustomError(crate::MyError),
 	}
 }
 
+#[derive(scale_info::TypeInfo, codec::Encode, codec::Decode)]
+enum MyError {}
+
 fn main() {
 }
diff --git a/frame/support/test/tests/pallet_ui/error_does_not_derive_pallet_error.stderr b/frame/support/test/tests/pallet_ui/error_does_not_derive_pallet_error.stderr
new file mode 100644
index 0000000000000..2a8149e309ac1
--- /dev/null
+++ b/frame/support/test/tests/pallet_ui/error_does_not_derive_pallet_error.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `MyError: PalletError` is not satisfied
+  --> tests/pallet_ui/error_does_not_derive_pallet_error.rs:1:1
+   |
+1  | #[frame_support::pallet]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `PalletError` is not implemented for `MyError`
+   |
+note: required by `MAX_ENCODED_SIZE`
+  --> $WORKSPACE/frame/support/src/traits/error.rs
+   |
+   |     const MAX_ENCODED_SIZE: usize;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: this error originates in the derive macro `frame_support::PalletError` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/frame/support/test/tests/pallet_ui/error_no_fieldless.stderr b/frame/support/test/tests/pallet_ui/error_no_fieldless.stderr
deleted file mode 100644
index 1d69fbeff9aac..0000000000000
--- a/frame/support/test/tests/pallet_ui/error_no_fieldless.stderr
+++ /dev/null
@@ -1,5 +0,0 @@
-error: Invalid pallet::error, unexpected fields, must be `Unit`
-  --> $DIR/error_no_fieldless.rs:20:5
-   |
-20 |         U8(u8),
-   |           ^^^^
diff --git a/frame/support/test/tests/pallet_ui/pass/error_nested_types.rs b/frame/support/test/tests/pallet_ui/pass/error_nested_types.rs
new file mode 100644
index 0000000000000..1b6f584af23b9
--- /dev/null
+++ b/frame/support/test/tests/pallet_ui/pass/error_nested_types.rs
@@ -0,0 +1,41 @@
+use codec::{Decode, Encode};
+use frame_support::PalletError;
+
+#[frame_support::pallet]
+mod pallet {
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+	#[pallet::error]
+	pub enum Error<T> {
+		CustomError(crate::MyError),
+	}
+}
+
+#[derive(Encode, Decode, PalletError, scale_info::TypeInfo)]
+pub enum MyError {
+    Foo,
+    Bar,
+    Baz(NestedError),
+    Struct(MyStruct),
+    Wrapper(Wrapper),
+}
+
+#[derive(Encode, Decode, PalletError, scale_info::TypeInfo)]
+pub enum NestedError {
+    Quux
+}
+
+#[derive(Encode, Decode, PalletError, scale_info::TypeInfo)]
+pub struct MyStruct {
+    field: u8,
+}
+
+#[derive(Encode, Decode, PalletError, scale_info::TypeInfo)]
+pub struct Wrapper(bool);
+
+fn main() {
+}
diff --git a/frame/utility/src/tests.rs b/frame/utility/src/tests.rs
index 9a1e11f54d6e3..44b07f70db14c 100644
--- a/frame/utility/src/tests.rs
+++ b/frame/utility/src/tests.rs
@@ -38,7 +38,6 @@ use sp_runtime::{
 // example module to test behaviors.
 #[frame_support::pallet]
 pub mod example {
-	use super::*;
 	use frame_support::{dispatch::WithPostDispatchInfo, pallet_prelude::*};
 	use frame_system::pallet_prelude::*;
 
diff --git a/primitives/block-builder/src/lib.rs b/primitives/block-builder/src/lib.rs
index 229f115c6667f..1b74c27b7ae43 100644
--- a/primitives/block-builder/src/lib.rs
+++ b/primitives/block-builder/src/lib.rs
@@ -20,11 +20,14 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 
 use sp_inherents::{CheckInherentsResult, InherentData};
-use sp_runtime::{traits::Block as BlockT, ApplyExtrinsicResult};
+use sp_runtime::{
+	legacy::byte_sized_error::ApplyExtrinsicResult as ApplyExtrinsicResultBeforeV6,
+	traits::Block as BlockT, ApplyExtrinsicResult,
+};
 
 sp_api::decl_runtime_apis! {
 	/// The `BlockBuilder` api trait that provides the required functionality for building a block.
-	#[api_version(5)]
+	#[api_version(6)]
 	pub trait BlockBuilder {
 		/// Apply the given extrinsic.
 		///
@@ -32,6 +35,9 @@ sp_api::decl_runtime_apis! {
 		/// this block or not.
 		fn apply_extrinsic(extrinsic: <Block as BlockT>::Extrinsic) -> ApplyExtrinsicResult;
 
+		#[changed_in(6)]
+		fn apply_extrinsic(extrinsic: <Block as BlockT>::Extrinsic) -> ApplyExtrinsicResultBeforeV6;
+
 		/// Finish the current block.
 		#[renamed("finalise_block", 3)]
 		fn finalize_block() -> <Block as BlockT>::Header;
diff --git a/primitives/runtime/src/legacy.rs b/primitives/runtime/src/legacy.rs
new file mode 100644
index 0000000000000..7bc7c88a7e10d
--- /dev/null
+++ b/primitives/runtime/src/legacy.rs
@@ -0,0 +1,20 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2022 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Runtime types that existed in old API versions.
+
+pub mod byte_sized_error;
diff --git a/primitives/runtime/src/legacy/byte_sized_error.rs b/primitives/runtime/src/legacy/byte_sized_error.rs
new file mode 100644
index 0000000000000..049abff69ff1a
--- /dev/null
+++ b/primitives/runtime/src/legacy/byte_sized_error.rs
@@ -0,0 +1,100 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2022 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Runtime types that existed prior to BlockBuilder API version 6.
+
+use crate::{ArithmeticError, TokenError};
+use codec::{Decode, Encode};
+use scale_info::TypeInfo;
+#[cfg(feature = "std")]
+use serde::{Deserialize, Serialize};
+
+/// [`ModuleError`] type definition before BlockBuilder API version 6.
+#[derive(Eq, Clone, Copy, Encode, Decode, Debug, TypeInfo)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub struct ModuleError {
+	/// Module index, matching the metadata module index.
+	pub index: u8,
+	/// Module specific error value.
+	pub error: u8,
+	/// Optional error message.
+	#[codec(skip)]
+	#[cfg_attr(feature = "std", serde(skip_deserializing))]
+	pub message: Option<&'static str>,
+}
+
+impl PartialEq for ModuleError {
+	fn eq(&self, other: &Self) -> bool {
+		(self.index == other.index) && (self.error == other.error)
+	}
+}
+
+/// [`DispatchError`] type definition before BlockBuilder API version 6.
+#[derive(Eq, Clone, Copy, Encode, Decode, Debug, TypeInfo, PartialEq)]
+#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
+pub enum DispatchError {
+	/// Some error occurred.
+	Other(
+		#[codec(skip)]
+		#[cfg_attr(feature = "std", serde(skip_deserializing))]
+		&'static str,
+	),
+	/// Failed to lookup some data.
+	CannotLookup,
+	/// A bad origin.
+	BadOrigin,
+	/// A custom error in a module.
+	Module(ModuleError),
+	/// At least one consumer is remaining so the account cannot be destroyed.
+	ConsumerRemaining,
+	/// There are no providers so the account cannot be created.
+	NoProviders,
+	/// There are too many consumers so the account cannot be created.
+	TooManyConsumers,
+	/// An error to do with tokens.
+	Token(TokenError),
+	/// An arithmetic error.
+	Arithmetic(ArithmeticError),
+}
+
+/// [`DispatchOutcome`] type definition before BlockBuilder API version 6.
+pub type DispatchOutcome = Result<(), DispatchError>;
+
+/// [`ApplyExtrinsicResult`] type definition before BlockBuilder API version 6.
+pub type ApplyExtrinsicResult =
+	Result<DispatchOutcome, crate::transaction_validity::TransactionValidityError>;
+
+/// Convert the legacy `ApplyExtrinsicResult` type to the latest version.
+pub fn convert_to_latest(old: ApplyExtrinsicResult) -> crate::ApplyExtrinsicResult {
+	old.map(|outcome| {
+		outcome.map_err(|e| match e {
+			DispatchError::Other(s) => crate::DispatchError::Other(s),
+			DispatchError::CannotLookup => crate::DispatchError::CannotLookup,
+			DispatchError::BadOrigin => crate::DispatchError::BadOrigin,
+			DispatchError::Module(err) => crate::DispatchError::Module(crate::ModuleError {
+				index: err.index,
+				error: [err.error, 0, 0, 0],
+				message: err.message,
+			}),
+			DispatchError::ConsumerRemaining => crate::DispatchError::ConsumerRemaining,
+			DispatchError::NoProviders => crate::DispatchError::NoProviders,
+			DispatchError::TooManyConsumers => crate::DispatchError::TooManyConsumers,
+			DispatchError::Token(err) => crate::DispatchError::Token(err),
+			DispatchError::Arithmetic(err) => crate::DispatchError::Arithmetic(err),
+		})
+	})
+}
diff --git a/primitives/runtime/src/lib.rs b/primitives/runtime/src/lib.rs
index a428da59f6a0d..337fac5812aed 100644
--- a/primitives/runtime/src/lib.rs
+++ b/primitives/runtime/src/lib.rs
@@ -57,6 +57,7 @@ use scale_info::TypeInfo;
 
 pub mod curve;
 pub mod generic;
+pub mod legacy;
 mod multiaddress;
 pub mod offchain;
 pub mod runtime_logger;
@@ -97,6 +98,10 @@ pub use sp_arithmetic::{
 
 pub use either::Either;
 
+/// The number of bytes of the module-specific `error` field defined in [`ModuleError`].
+/// In FRAME, this is the maximum encoded size of a pallet error type.
+pub const MAX_MODULE_ERROR_ENCODED_SIZE: usize = 4;
+
 /// An abstraction over justification for a block's validity under a consensus algorithm.
 ///
 /// Essentially a finality proof. The exact formulation will vary between consensus
@@ -468,7 +473,7 @@ pub struct ModuleError {
 	/// Module index, matching the metadata module index.
 	pub index: u8,
 	/// Module specific error value.
-	pub error: u8,
+	pub error: [u8; MAX_MODULE_ERROR_ENCODED_SIZE],
 	/// Optional error message.
 	#[codec(skip)]
 	#[cfg_attr(feature = "std", serde(skip_deserializing))]
@@ -922,15 +927,15 @@ mod tests {
 	fn dispatch_error_encoding() {
 		let error = DispatchError::Module(ModuleError {
 			index: 1,
-			error: 2,
+			error: [2, 0, 0, 0],
 			message: Some("error message"),
 		});
 		let encoded = error.encode();
 		let decoded = DispatchError::decode(&mut &encoded[..]).unwrap();
-		assert_eq!(encoded, vec![3, 1, 2]);
+		assert_eq!(encoded, vec![3, 1, 2, 0, 0, 0]);
 		assert_eq!(
 			decoded,
-			DispatchError::Module(ModuleError { index: 1, error: 2, message: None })
+			DispatchError::Module(ModuleError { index: 1, error: [2, 0, 0, 0], message: None })
 		);
 	}
 
@@ -943,9 +948,9 @@ mod tests {
 			Other("bar"),
 			CannotLookup,
 			BadOrigin,
-			Module(ModuleError { index: 1, error: 1, message: None }),
-			Module(ModuleError { index: 1, error: 2, message: None }),
-			Module(ModuleError { index: 2, error: 1, message: None }),
+			Module(ModuleError { index: 1, error: [1, 0, 0, 0], message: None }),
+			Module(ModuleError { index: 1, error: [2, 0, 0, 0], message: None }),
+			Module(ModuleError { index: 2, error: [1, 0, 0, 0], message: None }),
 			ConsumerRemaining,
 			NoProviders,
 			Token(TokenError::NoFunds),
@@ -970,8 +975,8 @@ mod tests {
 
 		// Ignores `message` field in `Module` variant.
 		assert_eq!(
-			Module(ModuleError { index: 1, error: 1, message: Some("foo") }),
-			Module(ModuleError { index: 1, error: 1, message: None }),
+			Module(ModuleError { index: 1, error: [1, 0, 0, 0], message: Some("foo") }),
+			Module(ModuleError { index: 1, error: [1, 0, 0, 0], message: None }),
 		);
 	}
 
diff --git a/primitives/runtime/src/traits.rs b/primitives/runtime/src/traits.rs
index 1cea7c4e805c1..ba4ca790a9198 100644
--- a/primitives/runtime/src/traits.rs
+++ b/primitives/runtime/src/traits.rs
@@ -1554,6 +1554,12 @@ impl Printable for &[u8] {
 	}
 }
 
+impl<const N: usize> Printable for [u8; N] {
+	fn print(&self) {
+		sp_io::misc::print_hex(&self[..]);
+	}
+}
+
 impl Printable for &str {
 	fn print(&self) {
 		sp_io::misc::print_utf8(self.as_bytes());
diff --git a/utils/frame/rpc/system/src/lib.rs b/utils/frame/rpc/system/src/lib.rs
index eb1b258c97ec6..0eae4d061afbb 100644
--- a/utils/frame/rpc/system/src/lib.rs
+++ b/utils/frame/rpc/system/src/lib.rs
@@ -25,10 +25,11 @@ use jsonrpc_core::{Error as RpcError, ErrorCode};
 use jsonrpc_derive::rpc;
 use sc_rpc_api::DenyUnsafe;
 use sc_transaction_pool_api::{InPoolTransaction, TransactionPool};
+use sp_api::ApiExt;
 use sp_block_builder::BlockBuilder;
 use sp_blockchain::HeaderBackend;
 use sp_core::{hexdisplay::HexDisplay, Bytes};
-use sp_runtime::{generic::BlockId, traits};
+use sp_runtime::{generic::BlockId, legacy, traits};
 
 pub use self::gen_client::Client as SystemClient;
 pub use frame_system_rpc_runtime_api::AccountNonceApi;
@@ -135,14 +136,40 @@ where
 				.map_err(|e| RpcError {
 					code: ErrorCode::ServerError(Error::DecodeError.into()),
 					message: "Unable to dry run extrinsic.".into(),
-					data: Some(format!("{:?}", e).into()),
+					data: Some(e.to_string().into()),
 				})?;
 
-			let result = api.apply_extrinsic(&at, uxt).map_err(|e| RpcError {
-				code: ErrorCode::ServerError(Error::RuntimeError.into()),
-				message: "Unable to dry run extrinsic.".into(),
-				data: Some(e.to_string().into()),
-			})?;
+			let api_version = api
+				.api_version::<dyn BlockBuilder<Block>>(&at)
+				.map_err(|e| RpcError {
+					code: ErrorCode::ServerError(Error::RuntimeError.into()),
+					message: "Unable to dry run extrinsic.".into(),
+					data: Some(e.to_string().into()),
+				})?
+				.ok_or_else(|| RpcError {
+					code: ErrorCode::ServerError(Error::RuntimeError.into()),
+					message: "Unable to dry run extrinsic.".into(),
+					data: Some(
+						format!("Could not find `BlockBuilder` api for block `{:?}`.", at).into(),
+					),
+				})?;
+
+			let result = if api_version < 6 {
+				#[allow(deprecated)]
+				api.apply_extrinsic_before_version_6(&at, uxt)
+					.map(legacy::byte_sized_error::convert_to_latest)
+					.map_err(|e| RpcError {
+						code: ErrorCode::ServerError(Error::RuntimeError.into()),
+						message: "Unable to dry run extrinsic.".into(),
+						data: Some(e.to_string().into()),
+					})?
+			} else {
+				api.apply_extrinsic(&at, uxt).map_err(|e| RpcError {
+					code: ErrorCode::ServerError(Error::RuntimeError.into()),
+					message: "Unable to dry run extrinsic.".into(),
+					data: Some(e.to_string().into()),
+				})?
+			};
 
 			Ok(Encode::encode(&result).into())
 		};