diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index 4926f0012c6..06cb6b62adc 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -2469,12 +2469,9 @@ DefineConstructorAndPrototype(JSContext *cx, HandleObject obj, JSProtoKey key, H
 
     /*
      * Create the prototype object.  (GlobalObject::createBlankPrototype isn't
-     * used because it parents the prototype object to the global and because
-     * it uses WithProto::Given.  FIXME: Undo dependencies on this parentage
-     * [which already needs to happen for bug 638316], figure out nicer
-     * semantics for null-protoProto, and use createBlankPrototype.)
+     * used because it won't let us use protoProto as the proto.
      */
-    RootedNativeObject proto(cx, NewNativeObjectWithClassProto(cx, clasp, protoProto, obj, SingletonObject));
+    RootedNativeObject proto(cx, NewNativeObjectWithClassProto(cx, clasp, protoProto, SingletonObject));
     if (!proto)
         return nullptr;
 
diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index bab1b49a096..5d8d81930a9 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -166,8 +166,7 @@ js::OnUnknownMethod(JSContext *cx, HandleObject obj, Value idval_, MutableHandle
         return false;
 
     if (value.isObject()) {
-        NativeObject *obj = NewNativeObjectWithClassProto(cx, &js_NoSuchMethodClass, NullPtr(),
-                                                          NullPtr());
+        NativeObject *obj = NewNativeObjectWithClassProto(cx, &js_NoSuchMethodClass, NullPtr());
         if (!obj)
             return false;
 
diff --git a/js/src/vm/NativeObject-inl.h b/js/src/vm/NativeObject-inl.h
index c1cc0157687..6baecb717f7 100644
--- a/js/src/vm/NativeObject-inl.h
+++ b/js/src/vm/NativeObject-inl.h
@@ -376,17 +376,17 @@ NewNativeObjectWithGivenProto(ExclusiveContext *cx, const Class *clasp,
 
 inline NativeObject *
 NewNativeObjectWithClassProto(ExclusiveContext *cx, const Class *clasp, HandleObject proto,
-                              HandleObject parent, gc::AllocKind allocKind,
+                              gc::AllocKind allocKind,
                               NewObjectKind newKind = GenericObject)
 {
-    return MaybeNativeObject(NewObjectWithClassProto(cx, clasp, proto, parent, allocKind, newKind));
+    return MaybeNativeObject(NewObjectWithClassProto(cx, clasp, proto, NullPtr(), allocKind, newKind));
 }
 
 inline NativeObject *
 NewNativeObjectWithClassProto(ExclusiveContext *cx, const Class *clasp, HandleObject proto,
-                              HandleObject parent, NewObjectKind newKind = GenericObject)
+                              NewObjectKind newKind = GenericObject)
 {
-    return MaybeNativeObject(NewObjectWithClassProto(cx, clasp, proto, parent, newKind));
+    return MaybeNativeObject(NewObjectWithClassProto(cx, clasp, proto, NullPtr(), newKind));
 }
 
 /*