diff --git a/tasm-lib/src/list/higher_order/map.rs b/tasm-lib/src/list/higher_order/map.rs
index bd9ae1f5..95092f5b 100644
--- a/tasm-lib/src/list/higher_order/map.rs
+++ b/tasm-lib/src/list/higher_order/map.rs
@@ -33,6 +33,8 @@ use crate::traits::function::FunctionInitialState;
 
 const INNER_FN_INCORRECT_NUM_INPUTS: &str = "Inner function in `map` only works with *one* input. \
                                              Use a tuple as a workaround.";
+const INNER_FN_INCORRECT_INPUT_DYN_LEN: &str = "An input type of dynamic length to `map`s inner \
+                                                function must be a tuple of form `(bfe, _)`.";
 
 /// Applies a given function to every element of a list, and collects the new
 /// elements into a new list.
@@ -94,14 +96,24 @@ impl<const NUM_INPUT_LISTS: usize> ChainMap<NUM_INPUT_LISTS> {
     ///
     /// - if the input type has [static length] _and_ takes up
     ///     [`OpStackElement::COUNT`] or more words
+    /// - if the input type has dynamic length and is _anything but_ a tuple
+    ///     `(_, `[`BFieldElement`][bfe]`)`
     /// - if the output type takes up [`OpStackElement::COUNT`]` - 1` or more words
     /// - if the output type does not have a [static length][len]
     ///
     /// [len]: BFieldCodec::static_length
+    /// [bfe]: DataType::Bfe
     pub fn new(f: InnerFunction) -> Self {
         if let Some(input_len) = f.domain().static_length() {
             // need instruction `place {input_type.stack_size()}`
             assert!(input_len < OpStackElement::COUNT);
+        } else {
+            let DataType::Tuple(tuple) = f.domain() else {
+                panic!("{INNER_FN_INCORRECT_INPUT_DYN_LEN}");
+            };
+            let [_, DataType::Bfe] = tuple[..] else {
+                panic!("{INNER_FN_INCORRECT_INPUT_DYN_LEN}");
+            };
         }
 
         // need instruction `pick {output_type.stack_size() + 1}`
@@ -522,7 +534,6 @@ impl<const NUM_INPUT_LISTS: usize> Function for ChainMap<NUM_INPUT_LISTS> {
 
 #[cfg(test)]
 mod tests {
-
     use itertools::Itertools;
     use num_traits::Zero;
     use proptest_arbitrary_interop::arb;
@@ -928,9 +939,10 @@ mod tests {
     #[test]
     fn mapping_over_dynamic_length_items_works() {
         let f = || {
+            let list_type = DataType::List(Box::new(DataType::Bfe));
             InnerFunction::RawCode(RawCode::new(
                 triton_asm!(just_forty_twos: pop 2 push 42 return),
-                DataType::List(Box::new(DataType::Bfe)),
+                DataType::Tuple(vec![list_type, DataType::Bfe]),
                 DataType::Bfe,
             ))
         };
@@ -942,9 +954,10 @@ mod tests {
     #[test]
     fn mapping_over_list_of_lists_writing_their_lengths_works() {
         let f = || {
+            let list_type = DataType::List(Box::new(DataType::Bfe));
             InnerFunction::RawCode(RawCode::new(
                 triton_asm!(write_list_length: pop 1 read_mem 1 pop 1 return),
-                DataType::List(Box::new(DataType::Bfe)),
+                DataType::Tuple(vec![list_type, DataType::Bfe]),
                 DataType::Bfe,
             ))
         };
@@ -971,9 +984,10 @@ mod benches {
 
     #[test]
     fn map_with_dyn_items_benchmark() {
+        let list_type = DataType::List(Box::new(DataType::Bfe));
         let f = InnerFunction::RawCode(RawCode::new(
             triton_asm!(dyn_length_elements: pop 2 push 42 return),
-            DataType::List(Box::new(DataType::Bfe)),
+            DataType::Tuple(vec![list_type, DataType::Bfe]),
             DataType::Bfe,
         ));
         ShadowedFunction::new(Map::new(f)).bench();