diff --git a/src/builder/build_traits.rs b/src/builder/build_traits.rs
index a4deabbe2..734995a49 100644
--- a/src/builder/build_traits.rs
+++ b/src/builder/build_traits.rs
@@ -438,9 +438,8 @@ pub trait Dataflow: Container {
         let hugr = self.hugr();
         let def_op = hugr.get_optype(function.node());
         let signature = match def_op {
-            OpType::Def(ops::Def { signature }) | OpType::Declare(ops::Declare { signature }) => {
-                signature.clone()
-            }
+            OpType::Def(ops::Def { signature, .. })
+            | OpType::Declare(ops::Declare { signature, .. }) => signature.clone(),
             _ => {
                 return Err(BuildError::UnexpectedType {
                     node: function.node(),
diff --git a/src/builder/dataflow.rs b/src/builder/dataflow.rs
index 729e66728..9623a19c8 100644
--- a/src/builder/dataflow.rs
+++ b/src/builder/dataflow.rs
@@ -128,10 +128,13 @@ impl FunctionBuilder<HugrMut> {
     /// # Errors
     ///
     /// Error in adding DFG child nodes.
-    pub fn new(_name: impl Into<String>, signature: Signature) -> Result<Self, BuildError> {
+    pub fn new(name: impl Into<String>, signature: Signature) -> Result<Self, BuildError> {
         let inputs = signature.input.clone();
         let outputs = signature.output.clone();
-        let op = ops::Def { signature };
+        let op = ops::Def {
+            signature,
+            name: name.into(),
+        };
 
         let base = HugrMut::new(op);
         let root = base.hugr().root();
diff --git a/src/builder/module_builder.rs b/src/builder/module_builder.rs
index 7a426e432..abf5c8a0b 100644
--- a/src/builder/module_builder.rs
+++ b/src/builder/module_builder.rs
@@ -73,18 +73,24 @@ impl<T: HugrMutRef> ModuleBuilder<T> {
         f_id: &FuncID<false>,
     ) -> Result<FunctionBuilder<&mut HugrMut>, BuildError> {
         let f_node = f_id.node();
-        let (inputs, outputs) =
-            if let OpType::Declare(ops::Declare { signature }) = self.hugr().get_optype(f_node) {
-                (signature.input.clone(), signature.output.clone())
-            } else {
-                return Err(BuildError::UnexpectedType {
-                    node: f_node,
-                    op_desc: "OpType::Declare",
-                });
-            };
+        let (inputs, outputs, name) = if let OpType::Declare(ops::Declare { signature, name }) =
+            self.hugr().get_optype(f_node)
+        {
+            (
+                signature.input.clone(),
+                signature.output.clone(),
+                name.clone(),
+            )
+        } else {
+            return Err(BuildError::UnexpectedType {
+                node: f_node,
+                op_desc: "OpType::Declare",
+            });
+        };
         self.base().replace_op(
             f_node,
             ops::Def {
+                name,
                 signature: Signature::new_df(inputs.clone(), outputs.clone()),
             },
         );
@@ -117,11 +123,14 @@ impl<T: HugrMutRef> ModuleBuilder<T> {
     /// [`OpType::Declare`] node.
     pub fn declare(
         &mut self,
-        _name: impl Into<String>,
+        name: impl Into<String>,
         signature: Signature,
     ) -> Result<FuncID<false>, BuildError> {
-        // TODO add name and param names to metadata
-        let declare_n = self.add_child_op(ops::Declare { signature })?;
+        // TODO add param names to metadata
+        let declare_n = self.add_child_op(ops::Declare {
+            signature,
+            name: name.into(),
+        })?;
 
         Ok(declare_n.into())
     }
diff --git a/src/hugr/hugrmut.rs b/src/hugr/hugrmut.rs
index df1ef52c2..1c3e376ce 100644
--- a/src/hugr/hugrmut.rs
+++ b/src/hugr/hugrmut.rs
@@ -285,6 +285,7 @@ mod test {
             .add_op_with_parent(
                 module,
                 ops::Def {
+                    name: "main".into(),
                     signature: Signature::new_df(type_row![NAT], type_row![NAT, NAT]),
                 },
             )
diff --git a/src/hugr/validate.rs b/src/hugr/validate.rs
index ca51479d1..45420534b 100644
--- a/src/hugr/validate.rs
+++ b/src/hugr/validate.rs
@@ -775,6 +775,7 @@ mod test {
     /// Returns the hugr and the node index of the definition.
     fn make_simple_hugr(copies: usize) -> (HugrMut, Node) {
         let def_op: OpType = ops::Def {
+            name: "main".into(),
             signature: Signature::new_df(type_row![B], vec![B; copies]),
         }
         .into();
@@ -871,6 +872,7 @@ mod test {
     #[test]
     fn invalid_root() {
         let declare_op: OpType = ops::Declare {
+            name: "main".into(),
             signature: Default::default(),
         }
         .into();
@@ -943,7 +945,13 @@ mod test {
         // Add a definition without children
         let def_sig = Signature::new_df(type_row![B], type_row![B, B]);
         let new_def = b
-            .add_op_with_parent(root, ops::Def { signature: def_sig })
+            .add_op_with_parent(
+                root,
+                ops::Def {
+                    signature: def_sig,
+                    name: "main".into(),
+                },
+            )
             .unwrap();
         assert_matches!(
             b.hugr().validate(),
diff --git a/src/ops/module.rs b/src/ops/module.rs
index 0776f3b2c..676b8befa 100644
--- a/src/ops/module.rs
+++ b/src/ops/module.rs
@@ -27,6 +27,8 @@ impl OpTrait for Module {
 /// Children nodes are the body of the definition.
 #[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
 pub struct Def {
+    /// Name of function
+    pub name: String,
     /// Signature of the function
     pub signature: Signature,
 }
@@ -51,6 +53,8 @@ impl OpTrait for Def {
 /// External function declaration, linked at runtime.
 #[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
 pub struct Declare {
+    /// Name of function
+    pub name: String,
     /// Signature of the function
     pub signature: Signature,
 }