diff --git a/hugr-core/src/hugr/views/sibling_subgraph.rs b/hugr-core/src/hugr/views/sibling_subgraph.rs
index 53c92ed56..cc8caa01f 100644
--- a/hugr-core/src/hugr/views/sibling_subgraph.rs
+++ b/hugr-core/src/hugr/views/sibling_subgraph.rs
@@ -304,11 +304,9 @@ impl SiblingSubgraph {
             })
             .collect_vec();
         Signature::new(input, output).with_extension_delta(ExtensionSet::union_over(
-            self.nodes.iter().map(|n| {
-                hugr.signature(*n)
-                    .expect("all nodes must have dataflow signature")
-                    .extension_reqs
-            }),
+            self.nodes
+                .iter()
+                .map(|n| hugr.get_optype(*n).extension_delta()),
         ))
     }
 
@@ -729,14 +727,14 @@ pub enum InvalidSubgraphBoundary {
 
 #[cfg(test)]
 mod tests {
-    use std::error::Error;
-
     use cool_asserts::assert_matches;
 
     use crate::builder::inout_sig;
-    use crate::extension::PRELUDE_REGISTRY;
+    use crate::extension::{prelude, ExtensionRegistry};
+    use crate::ops::Const;
+    use crate::std_extensions::arithmetic::float_types::{self, ConstF64};
     use crate::std_extensions::logic;
-    use crate::utils::test_quantum_extension::{self, cx_gate};
+    use crate::utils::test_quantum_extension::{self, cx_gate, rz_f64};
     use crate::{
         builder::{
             BuildError, DFGBuilder, Dataflow, DataflowHugr, DataflowSubContainer, HugrBuilder,
@@ -778,22 +776,36 @@ mod tests {
         }
     }
 
+    /// A Module with a single function from three qubits to three qubits.
+    /// The function applies a CX gate to the first two qubits and a Rz gate (with a constant angle) to the last qubit.
     fn build_hugr() -> Result<(Hugr, Node), BuildError> {
         let mut mod_builder = ModuleBuilder::new();
         let func = mod_builder.declare(
             "test",
             Signature::new_endo(type_row![QB_T, QB_T, QB_T])
-                .with_extension_delta(test_quantum_extension::EXTENSION_ID)
+                .with_extension_delta(ExtensionSet::from_iter([
+                    test_quantum_extension::EXTENSION_ID,
+                    float_types::EXTENSION_ID,
+                ]))
                 .into(),
         )?;
         let func_id = {
             let mut dfg = mod_builder.define_declaration(&func)?;
             let [w0, w1, w2] = dfg.input_wires_arr();
             let [w0, w1] = dfg.add_dataflow_op(cx_gate(), [w0, w1])?.outputs_arr();
+            let c = dfg.add_load_const(Const::new(ConstF64::new(0.5).into()));
+            let [w2] = dfg.add_dataflow_op(rz_f64(), [w2, c])?.outputs_arr();
             dfg.finish_with_outputs([w0, w1, w2])?
         };
         let hugr = mod_builder
-            .finish_prelude_hugr()
+            .finish_hugr(
+                &ExtensionRegistry::try_new([
+                    prelude::PRELUDE.to_owned(),
+                    test_quantum_extension::EXTENSION.to_owned(),
+                    float_types::EXTENSION.to_owned(),
+                ])
+                .unwrap(),
+            )
             .map_err(|e| -> BuildError { e.into() })?;
         Ok((hugr, func_id.node()))
     }
@@ -888,16 +900,17 @@ mod tests {
         let sub = SiblingSubgraph::try_new_dataflow_subgraph(&func)?;
 
         let empty_dfg = {
-            let builder = DFGBuilder::new(Signature::new_endo(type_row![QB_T, QB_T])).unwrap();
+            let builder =
+                DFGBuilder::new(Signature::new_endo(type_row![QB_T, QB_T, QB_T])).unwrap();
             let inputs = builder.input_wires();
             builder.finish_prelude_hugr_with_outputs(inputs).unwrap()
         };
 
         let rep = sub.create_simple_replacement(&func, empty_dfg).unwrap();
 
-        assert_eq!(rep.subgraph().nodes().len(), 1);
+        assert_eq!(rep.subgraph().nodes().len(), 4);
 
-        assert_eq!(hugr.node_count(), 5); // Module + Def + In + CX + Out
+        assert_eq!(hugr.node_count(), 8); // Module + Def + In + CX + Rz + Const + LoadConst + Out
         hugr.apply_rewrite(rep).unwrap();
         assert_eq!(hugr.node_count(), 4); // Module + Def + In + Out
 
@@ -909,12 +922,14 @@ mod tests {
         let (hugr, dfg) = build_hugr().unwrap();
         let func: SiblingGraph<'_, FuncID<true>> = SiblingGraph::try_new(&hugr, dfg).unwrap();
         let sub = SiblingSubgraph::try_new_dataflow_subgraph(&func)?;
-        // The identity wire on the third qubit is ignored, so the subgraph's signature only contains
-        // the first two qubits.
         assert_eq!(
             sub.signature(&func),
-            Signature::new_endo(type_row![QB_T, QB_T])
-                .with_extension_delta(test_quantum_extension::EXTENSION_ID)
+            Signature::new_endo(type_row![QB_T, QB_T, QB_T]).with_extension_delta(
+                ExtensionSet::from_iter([
+                    test_quantum_extension::EXTENSION_ID,
+                    float_types::EXTENSION_ID,
+                ])
+            )
         );
         Ok(())
     }
@@ -947,7 +962,7 @@ mod tests {
                 .unwrap()
                 .nodes()
                 .len(),
-            1
+            4
         )
     }
 
@@ -1064,15 +1079,23 @@ mod tests {
     }
 
     #[test]
-    fn extract_subgraph() -> Result<(), Box<dyn Error>> {
-        let (hugr, func_root) = build_hugr()?;
-        let func_graph: SiblingGraph<'_, FuncID<true>> = SiblingGraph::try_new(&hugr, func_root)?;
-        let subgraph = SiblingSubgraph::try_new_dataflow_subgraph(&func_graph)?;
+    fn extract_subgraph() {
+        let (hugr, func_root) = build_hugr().unwrap();
+        let func_graph: SiblingGraph<'_, FuncID<true>> =
+            SiblingGraph::try_new(&hugr, func_root).unwrap();
+        let subgraph = SiblingSubgraph::try_new_dataflow_subgraph(&func_graph).unwrap();
         let extracted = subgraph.extract_subgraph(&hugr, "region");
 
-        extracted.validate(&PRELUDE_REGISTRY)?;
-
-        Ok(())
+        extracted
+            .validate(
+                &ExtensionRegistry::try_new([
+                    prelude::PRELUDE.to_owned(),
+                    test_quantum_extension::EXTENSION.to_owned(),
+                    float_types::EXTENSION.to_owned(),
+                ])
+                .unwrap(),
+            )
+            .unwrap();
     }
 
     #[test]