diff --git a/src/builder/build_traits.rs b/src/builder/build_traits.rs
index e3c0f6671..3a122eb8b 100644
--- a/src/builder/build_traits.rs
+++ b/src/builder/build_traits.rs
@@ -200,7 +200,7 @@ pub trait Dataflow: Container {
         op: impl Into<OpType>,
         input_wires: impl IntoIterator<Item = Wire>,
     ) -> Result<BuildHandle<DataflowOpID>, BuildError> {
-        self.add_dataflow_node(NodeType::new_open(op), input_wires)
+        self.add_dataflow_node(NodeType::new_default(op), input_wires)
     }
 
     /// Add a dataflow [`NodeType`] to the sibling graph, wiring up the `input_wires` to the
@@ -628,7 +628,7 @@ fn add_op_with_wires<T: Dataflow + ?Sized>(
     optype: impl Into<OpType>,
     inputs: Vec<Wire>,
 ) -> Result<(Node, usize), BuildError> {
-    add_node_with_wires(data_builder, NodeType::new_open(optype), inputs)
+    add_node_with_wires(data_builder, NodeType::new_default(optype), inputs)
 }
 
 fn add_node_with_wires<T: Dataflow + ?Sized>(
diff --git a/src/extension/infer.rs b/src/extension/infer.rs
index 46f2c0cad..d3fa0fa63 100644
--- a/src/extension/infer.rs
+++ b/src/extension/infer.rs
@@ -316,9 +316,6 @@ impl UnificationContext {
                         m_output,
                         node_type.op_signature().extension_reqs,
                     );
-                    if OpTag::ModuleOp.is_superset(node_type.tag()) {
-                        self.add_solution(m_input, ExtensionSet::new());
-                    }
                 }
                 // We have a solution for everything!
                 Some(sig) => {
diff --git a/src/hugr.rs b/src/hugr.rs
index c1acfb1fd..deccdada1 100644
--- a/src/hugr.rs
+++ b/src/hugr.rs
@@ -98,6 +98,17 @@ impl NodeType {
         }
     }
 
+    /// Instantiate an [OpType] with the default set of input extensions
+    /// for that OpType.
+    pub fn new_default(op: impl Into<OpType>) -> Self {
+        let op = op.into();
+        if OpTag::ModuleOp.is_superset(op.tag()) {
+            Self::new_pure(op)
+        } else {
+            Self::new_open(op)
+        }
+    }
+
     /// Use the input extensions to calculate the concrete signature of the node
     pub fn signature(&self) -> Option<Signature> {
         self.input_extensions
@@ -237,7 +248,7 @@ impl Hugr {
 
     /// Add a node to the graph, with the default conversion from OpType to NodeType
     pub(crate) fn add_op(&mut self, op: impl Into<OpType>) -> Node {
-        self.add_node(NodeType::new_open(op))
+        self.add_node(NodeType::new_default(op))
     }
 
     /// Add a node to the graph.
diff --git a/src/hugr/hugrmut.rs b/src/hugr/hugrmut.rs
index 52f47b309..7e066d1cb 100644
--- a/src/hugr/hugrmut.rs
+++ b/src/hugr/hugrmut.rs
@@ -37,7 +37,7 @@ pub trait HugrMut: HugrMutInternals {
         parent: Node,
         op: impl Into<OpType>,
     ) -> Result<Node, HugrError> {
-        self.add_node_with_parent(parent, NodeType::new_open(op))
+        self.add_node_with_parent(parent, NodeType::new_default(op))
     }
 
     /// Add a node to the graph with a parent in the hierarchy.
@@ -217,7 +217,7 @@ impl<T: RootTagged<RootHandle = Node> + AsMut<Hugr>> HugrMut for T {
     }
 
     fn add_op_before(&mut self, sibling: Node, op: impl Into<OpType>) -> Result<Node, HugrError> {
-        self.add_node_before(sibling, NodeType::new_open(op))
+        self.add_node_before(sibling, NodeType::new_default(op))
     }
 
     fn add_node_before(&mut self, sibling: Node, nodetype: NodeType) -> Result<Node, HugrError> {