--- a/js/src/vm/Shape.cpp
+++ b/js/src/vm/Shape.cpp
@@ -2016,17 +2016,17 @@ Shape::dumpSubtree(int level, js::Generi
             }
         }
     }
 }
 
 #endif
 
 static bool
-IsOriginalProto(GlobalObject* global, JSProtoKey key, JSObject& proto)
+IsOriginalProto(GlobalObject* global, JSProtoKey key, NativeObject& proto)
 {
     if (global->getPrototype(key) != ObjectValue(proto))
         return false;
 
     if (key == JSProto_Object) {
         MOZ_ASSERT(proto.staticPrototypeIsImmutable(),
                    "proto should be Object.prototype, whose prototype is "
                    "immutable");
@@ -2046,19 +2046,19 @@ IsOriginalProto(GlobalObject* global, JS
     MOZ_ASSERT(protoProto->staticPrototype() == nullptr,
                "Object.prototype must have null prototype");
     return true;
 }
 
 static JSProtoKey
 GetInitialShapeProtoKey(TaggedProto proto, JSContext* cx)
 {
-    if (proto.isObject() && proto.toObject()->hasStaticPrototype()) {
+    if (proto.isObject() && proto.toObject()->isNative()) {
         GlobalObject* global = cx->global();
-        JSObject& obj = *proto.toObject();
+        NativeObject& obj = proto.toObject()->as<NativeObject>();
         MOZ_ASSERT(global == &obj.global());
 
         if (IsOriginalProto(global, JSProto_Object, obj))
             return JSProto_Object;
         if (IsOriginalProto(global, JSProto_Function, obj))
             return JSProto_Function;
         if (IsOriginalProto(global, JSProto_Array, obj))
             return JSProto_Array;