diff --git a/src/extension/infer.rs b/src/extension/infer.rs
index 806d55726..bcea6175f 100644
--- a/src/extension/infer.rs
+++ b/src/extension/infer.rs
@@ -261,7 +261,7 @@ impl UnificationContext {
     where
         T: HugrView,
     {
-        if hugr.root_type().signature().is_none() {
+        if hugr.root_type().input_extensions().is_none() {
             let m_input = self.make_or_get_meta(hugr.root(), Direction::Incoming);
             self.variables.insert(m_input);
         }
@@ -302,7 +302,7 @@ impl UnificationContext {
                 self.add_constraint(m_output, Constraint::Equal(m_exit));
             }
 
-            match node_type.signature() {
+            match node_type.io_extensions() {
                 // Input extensions are open
                 None => {
                     let c = if let Some(sig) = node_type.op_signature() {
@@ -318,9 +318,9 @@ impl UnificationContext {
                     self.add_constraint(m_output, c);
                 }
                 // We have a solution for everything!
-                Some(sig) => {
-                    self.add_solution(m_output, sig.output_extensions());
-                    self.add_solution(m_input, sig.input_extensions);
+                Some((input_exts, output_exts)) => {
+                    self.add_solution(m_input, input_exts.clone());
+                    self.add_solution(m_output, output_exts);
                 }
             }
         }
diff --git a/src/extension/infer/test.rs b/src/extension/infer/test.rs
index 7a30da09d..0315ae353 100644
--- a/src/extension/infer/test.rs
+++ b/src/extension/infer/test.rs
@@ -253,26 +253,10 @@ fn dangling_src() -> Result<(), Box<dyn Error>> {
 
     let closure = hugr.infer_extensions()?;
     assert!(closure.is_empty());
+    assert_eq!(hugr.get_nodetype(src.node()).io_extensions().unwrap().1, rs);
     assert_eq!(
-        hugr.get_nodetype(src.node())
-            .signature()
-            .unwrap()
-            .output_extensions(),
-        rs
-    );
-    assert_eq!(
-        hugr.get_nodetype(mult.node())
-            .signature()
-            .unwrap()
-            .input_extensions,
-        rs
-    );
-    assert_eq!(
-        hugr.get_nodetype(mult.node())
-            .signature()
-            .unwrap()
-            .output_extensions(),
-        rs
+        hugr.get_nodetype(mult.node()).io_extensions().unwrap(),
+        (&rs.clone(), rs)
     );
     Ok(())
 }
@@ -385,18 +369,12 @@ fn test_conditional_inference() -> Result<(), Box<dyn Error>> {
 
     for node in [case0_node, case1_node, conditional_node] {
         assert_eq!(
-            hugr.get_nodetype(node)
-                .signature()
-                .unwrap()
-                .input_extensions,
-            ExtensionSet::new()
+            hugr.get_nodetype(node).io_extensions().unwrap().0,
+            &ExtensionSet::new()
         );
         assert_eq!(
-            hugr.get_nodetype(node)
-                .signature()
-                .unwrap()
-                .input_extensions,
-            ExtensionSet::new()
+            hugr.get_nodetype(node).io_extensions().unwrap().0,
+            &ExtensionSet::new()
         );
     }
     Ok(())
diff --git a/src/extension/validate.rs b/src/extension/validate.rs
index 2f267edf9..c66f777fa 100644
--- a/src/extension/validate.rs
+++ b/src/extension/validate.rs
@@ -50,13 +50,15 @@ impl ExtensionValidator {
     /// extension requirements for all of its input and output edges, then put
     /// those requirements in the extension validation context.
     fn gather_extensions(&mut self, node: &Node, node_type: &NodeType) {
-        if let Some(sig) = node_type.signature() {
-            for dir in Direction::BOTH {
-                assert!(self
-                    .extensions
-                    .insert((*node, dir), sig.get_extension(&dir))
-                    .is_none());
-            }
+        if let Some((input_exts, output_exts)) = node_type.io_extensions() {
+            let prev_i = self
+                .extensions
+                .insert((*node, Direction::Incoming), input_exts.clone());
+            assert!(prev_i.is_none());
+            let prev_o = self
+                .extensions
+                .insert((*node, Direction::Outgoing), output_exts);
+            assert!(prev_o.is_none());
         }
     }
 
diff --git a/src/hugr.rs b/src/hugr.rs
index 33f02dc43..474927d5b 100644
--- a/src/hugr.rs
+++ b/src/hugr.rs
@@ -31,7 +31,7 @@ use crate::extension::{
 };
 use crate::ops::custom::resolve_extension_ops;
 use crate::ops::{OpTag, OpTrait, OpType, DEFAULT_OPTYPE};
-use crate::types::{FunctionType, Signature};
+use crate::types::FunctionType;
 use crate::{Direction, Node};
 
 use delegate::delegate;
@@ -109,16 +109,6 @@ impl NodeType {
         }
     }
 
-    /// Use the input extensions to calculate the concrete signature of the node
-    pub fn signature(&self) -> Option<Signature> {
-        self.input_extensions.as_ref().map(|rs| {
-            self.op
-                .dataflow_signature()
-                .unwrap_or_default()
-                .with_input_extensions(rs.clone())
-        })
-    }
-
     /// Get the function type from the embedded op
     pub fn op_signature(&self) -> Option<FunctionType> {
         self.op.dataflow_signature()
@@ -134,6 +124,23 @@ impl NodeType {
         self.input_extensions.as_ref()
     }
 
+    /// The input and output extensions for this node, if set.
+    ///
+    /// `None`` if the [Self::input_extensions] is `None`.
+    /// Otherwise, will return Some, with the output extensions computed from the node's delta
+    pub fn io_extensions(&self) -> Option<(&ExtensionSet, ExtensionSet)> {
+        self.input_extensions.as_ref().map(|e| {
+            (
+                e,
+                self.op
+                    .dataflow_signature()
+                    .map(|ft| ft.extension_reqs)
+                    .unwrap_or_default()
+                    .union(e),
+            )
+        })
+    }
+
     /// Gets the underlying [OpType] i.e. without any [input_extensions]
     ///
     /// [input_extensions]: NodeType::input_extensions
@@ -411,19 +418,10 @@ mod test {
         hugr.infer_extensions()?;
 
         assert_eq!(
-            hugr.get_nodetype(lift)
-                .signature()
-                .unwrap()
-                .input_extensions,
-            ExtensionSet::new()
-        );
-        assert_eq!(
-            hugr.get_nodetype(output)
-                .signature()
-                .unwrap()
-                .input_extensions,
-            r
+            hugr.get_nodetype(lift).input_extensions().unwrap(),
+            &ExtensionSet::new()
         );
+        assert_eq!(hugr.get_nodetype(output).input_extensions().unwrap(), &r);
         Ok(())
     }
 }
diff --git a/src/types/signature.rs b/src/types/signature.rs
index 6e4c6b60c..fe91ccfde 100644
--- a/src/types/signature.rs
+++ b/src/types/signature.rs
@@ -27,7 +27,7 @@ pub struct FunctionType {
 }
 
 #[derive(Clone, Default, Debug, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
-/// A concrete signature, which has been instantiated with a set of input extensions
+/// A combination of a FunctionType and a set of input extensions, used for declaring functions
 pub struct Signature {
     /// The underlying signature
     pub signature: FunctionType,
@@ -243,15 +243,6 @@ impl FunctionType {
 }
 
 impl Signature {
-    /// Returns a reference to the extension set for the ports of the
-    /// signature in a given direction
-    pub fn get_extension(&self, dir: &Direction) -> ExtensionSet {
-        match dir {
-            Direction::Incoming => self.input_extensions.clone(),
-            Direction::Outgoing => self.output_extensions(),
-        }
-    }
-
     delegate! {
         to self.signature {
             /// Inputs of the function type