diff --git a/components/script/dom/testbinding.rs b/components/script/dom/testbinding.rs
index 3be8597ed413..d9defc537707 100644
--- a/components/script/dom/testbinding.rs
+++ b/components/script/dom/testbinding.rs
@@ -436,6 +436,8 @@ impl TestBindingMethods for TestBinding {
     fn PassUnion7(&self, _: StringSequenceOrUnsignedLong) {}
     fn PassUnion8(&self, _: ByteStringSequenceOrLong) {}
     fn PassUnion9(&self, _: RootedTraceableBox<UnionTypes::TestDictionaryOrLong>) {}
+    #[allow(unsafe_code)]
+    unsafe fn PassUnion10(&self, _: *mut JSContext, _: RootedTraceableBox<UnionTypes::StringOrObject>) {}
     fn PassUnionWithTypedef(&self, _: DocumentOrTestTypedef) {}
     fn PassUnionWithTypedef2(&self, _: LongSequenceOrTestTypedef) {}
     #[allow(unsafe_code)]
diff --git a/components/script/dom/webidls/TestBinding.webidl b/components/script/dom/webidls/TestBinding.webidl
index fc6d47713669..742169479179 100644
--- a/components/script/dom/webidls/TestBinding.webidl
+++ b/components/script/dom/webidls/TestBinding.webidl
@@ -246,6 +246,7 @@ interface TestBinding {
   void passUnion7((sequence<DOMString> or unsigned long) arg);
   void passUnion8((sequence<ByteString> or long) arg);
   void passUnion9((TestDictionary or long) arg);
+  void passUnion10((DOMString or object) arg);
   void passUnionWithTypedef((Document or TestTypedef) arg);
   void passUnionWithTypedef2((sequence<long> or TestTypedef) arg);
   void passAny(any arg);