diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index e5c3761edfe..9846cdd7b97 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -6127,7 +6127,7 @@ class CGBindingRoot(CGThing):
                 cgthings.extend([CGGeneric("\npub use dom::bindings::codegen::UnionTypes::%s as %s;\n\n" %
                                            (t.innerType, t.identifier.name))])
             else:
-                assert not typeNeedsRooting(t.innerType, config.getDescriptorProvider)
+                assert not typeNeedsRooting(t.innerType, config.getDescriptorProvider())
                 cgthings.extend([CGGeneric("\npub type %s = " % (t.identifier.name)),
                                  getRetvalDeclarationForType(t.innerType, config.getDescriptorProvider()),
                                  CGGeneric(";\n\n")])
diff --git a/components/script/dom/webidls/TestBinding.webidl b/components/script/dom/webidls/TestBinding.webidl
index 59d4fb35466..d688c0d96b6 100644
--- a/components/script/dom/webidls/TestBinding.webidl
+++ b/components/script/dom/webidls/TestBinding.webidl
@@ -8,6 +8,7 @@
 enum TestEnum { "", "foo", "bar" };
 typedef (DOMString or URL or Blob) TestTypedef;
 typedef (DOMString or URL or Blob)? TestTypedefNullableUnion;
+typedef DOMString TestTypedefString;
 
 dictionary TestDictionary {
   required boolean requiredValue;