diff --git a/hugr-core/src/builder/build_traits.rs b/hugr-core/src/builder/build_traits.rs
index 9703d65c3..9279a6ba5 100644
--- a/hugr-core/src/builder/build_traits.rs
+++ b/hugr-core/src/builder/build_traits.rs
@@ -429,6 +429,7 @@ pub trait Dataflow: Container {
         just_inputs: impl IntoIterator<Item = (Type, Wire)>,
         inputs_outputs: impl IntoIterator<Item = (Type, Wire)>,
         just_out_types: TypeRow,
+        extension_delta: ExtensionSet,
     ) -> Result<TailLoopBuilder<&mut Hugr>, BuildError> {
         let (input_types, mut input_wires): (Vec<Type>, Vec<Wire>) =
             just_inputs.into_iter().unzip();
@@ -440,6 +441,7 @@ pub trait Dataflow: Container {
             just_inputs: input_types.into(),
             just_outputs: just_out_types,
             rest: rest_types.into(),
+            extension_delta,
         };
         // TODO: Make input extensions a parameter
         let (loop_node, _) = add_node_with_wires(self, tail_loop.clone(), input_wires)?;
diff --git a/hugr-core/src/builder/tail_loop.rs b/hugr-core/src/builder/tail_loop.rs
index 901324fe9..3f41574b5 100644
--- a/hugr-core/src/builder/tail_loop.rs
+++ b/hugr-core/src/builder/tail_loop.rs
@@ -1,3 +1,4 @@
+use crate::extension::ExtensionSet;
 use crate::ops;
 
 use crate::hugr::{views::HugrView, NodeType};
@@ -74,11 +75,13 @@ impl TailLoopBuilder<Hugr> {
         just_inputs: impl Into<TypeRow>,
         inputs_outputs: impl Into<TypeRow>,
         just_outputs: impl Into<TypeRow>,
+        extension_delta: ExtensionSet,
     ) -> Result<Self, BuildError> {
         let tail_loop = ops::TailLoop {
             just_inputs: just_inputs.into(),
             just_outputs: just_outputs.into(),
             rest: inputs_outputs.into(),
+            extension_delta,
         };
         // TODO: Allow input extensions to be specified
         let base = Hugr::new(NodeType::new_open(tail_loop.clone()));
@@ -97,7 +100,6 @@ mod test {
             DataflowSubContainer, HugrBuilder, ModuleBuilder,
         },
         extension::prelude::{ConstUsize, PRELUDE_ID, USIZE_T},
-        extension::ExtensionSet,
         hugr::ValidationError,
         ops::Value,
         type_row,
@@ -107,7 +109,8 @@ mod test {
     #[test]
     fn basic_loop() -> Result<(), BuildError> {
         let build_result: Result<Hugr, ValidationError> = {
-            let mut loop_b = TailLoopBuilder::new(vec![], vec![BIT], vec![USIZE_T])?;
+            let mut loop_b =
+                TailLoopBuilder::new(vec![], vec![BIT], vec![USIZE_T], PRELUDE_ID.into())?;
             let [i1] = loop_b.input_wires_arr();
             let const_wire = loop_b.add_load_value(ConstUsize::new(1));
 
@@ -141,8 +144,12 @@ mod test {
                     )?
                     .outputs_arr();
                 let loop_id = {
-                    let mut loop_b =
-                        fbuild.tail_loop_builder(vec![(BIT, b1)], vec![], type_row![NAT])?;
+                    let mut loop_b = fbuild.tail_loop_builder(
+                        vec![(BIT, b1)],
+                        vec![],
+                        type_row![NAT],
+                        PRELUDE_ID.into(),
+                    )?;
                     let signature = loop_b.loop_signature()?.clone();
                     let const_val = Value::true_val();
                     let const_wire = loop_b.add_load_const(Value::true_val());
@@ -161,7 +168,7 @@ mod test {
                             ([type_row![], type_row![]], const_wire),
                             vec![(BIT, b1)],
                             output_row,
-                            ExtensionSet::new(),
+                            PRELUDE_ID.into(),
                         )?;
 
                         let mut branch_0 = conditional_b.case_builder(0)?;
diff --git a/hugr-core/src/ops.rs b/hugr-core/src/ops.rs
index 2e48d1f9d..76f3e54a4 100644
--- a/hugr-core/src/ops.rs
+++ b/hugr-core/src/ops.rs
@@ -432,7 +432,6 @@ impl OpParent for MakeTuple {}
 impl OpParent for UnpackTuple {}
 impl OpParent for Tag {}
 impl OpParent for Lift {}
-impl OpParent for TailLoop {}
 impl OpParent for CFG {}
 impl OpParent for Conditional {}
 impl OpParent for FuncDecl {}
diff --git a/hugr-core/src/ops/controlflow.rs b/hugr-core/src/ops/controlflow.rs
index 2aba3667a..b1a6b0e37 100644
--- a/hugr-core/src/ops/controlflow.rs
+++ b/hugr-core/src/ops/controlflow.rs
@@ -18,6 +18,8 @@ pub struct TailLoop {
     pub just_outputs: TypeRow,
     /// Types that are appended to both input and output
     pub rest: TypeRow,
+    /// Extension requirements to execute the body
+    pub extension_delta: ExtensionSet,
 }
 
 impl_op_name!(TailLoop);
@@ -32,7 +34,7 @@ impl DataflowOpTrait for TailLoop {
     fn signature(&self) -> FunctionType {
         let [inputs, outputs] =
             [&self.just_inputs, &self.just_outputs].map(|row| row.extend(self.rest.iter()));
-        FunctionType::new(inputs, outputs)
+        FunctionType::new(inputs, outputs).with_extension_delta(self.extension_delta.clone())
     }
 }
 
@@ -51,6 +53,13 @@ impl TailLoop {
     }
 }
 
+impl DataflowParent for TailLoop {
+    fn inner_signature(&self) -> FunctionType {
+        FunctionType::new(self.body_input_row(), self.body_output_row())
+            .with_extension_delta(self.extension_delta.clone())
+    }
+}
+
 /// Conditional operation, defined by child `Case` nodes for each branch.
 #[derive(Clone, Debug, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
 #[cfg_attr(test, derive(proptest_derive::Arbitrary))]
diff --git a/hugr-core/src/ops/validate.rs b/hugr-core/src/ops/validate.rs
index c87034d60..aaee46049 100644
--- a/hugr-core/src/ops/validate.rs
+++ b/hugr-core/src/ops/validate.rs
@@ -106,31 +106,6 @@ impl ValidateOp for super::Conditional {
     }
 }
 
-impl ValidateOp for super::TailLoop {
-    fn validity_flags(&self) -> OpValidityFlags {
-        OpValidityFlags {
-            allowed_children: OpTag::DataflowChild,
-            allowed_first_child: OpTag::Input,
-            allowed_second_child: OpTag::Output,
-            requires_children: true,
-            requires_dag: true,
-            ..Default::default()
-        }
-    }
-
-    fn validate_op_children<'a>(
-        &self,
-        children: impl DoubleEndedIterator<Item = (NodeIndex, &'a OpType)>,
-    ) -> Result<(), ChildrenValidationError> {
-        validate_io_nodes(
-            &self.body_input_row(),
-            &self.body_output_row(),
-            "tail-controlled loop graph",
-            children,
-        )
-    }
-}
-
 impl ValidateOp for super::CFG {
     fn validity_flags(&self) -> OpValidityFlags {
         OpValidityFlags {