diff --git a/src/hugr/validate.rs b/src/hugr/validate.rs
index cea7425bd..5d55022d0 100644
--- a/src/hugr/validate.rs
+++ b/src/hugr/validate.rs
@@ -997,8 +997,9 @@ mod test {
             .map_into()
             .collect_tuple()
             .unwrap();
-        let mut closure = b.infer_extensions().unwrap();
-        assert!(closure.remove(&copy).is_some());
+        let closure = b.infer_extensions().unwrap();
+        b.instantiate_extensions(closure);
+        b.validate(&EMPTY_REG).unwrap();
         b.replace_op(
             copy,
             NodeType::pure(ops::CFG {
@@ -1010,7 +1011,7 @@ mod test {
         // (i.e. update_and_validate) on such a malformed Hugr, and pure `validate(&EMPTY_REG)`
         // fails because of missing extension annotations (contained in the closure)
         assert_matches!(
-            b.validate_with_extension_closure(closure, &EMPTY_REG),
+            b.validate(&EMPTY_REG),
             Err(ValidationError::ContainerWithoutChildren { .. })
         );
         let cfg = copy;