--- a/js/src/vm/Shape.cpp
+++ b/js/src/vm/Shape.cpp
@@ -635,22 +635,17 @@ js::NewReshapedObject(JSContext *cx, Han
         while (!nshape->isEmptyShape()) {
             ids[nshape->slot()].set(nshape->propid());
             nshape = nshape->previous();
         }
     }
 
     /* Construct the new shape, without updating type information. */
     RootedId id(cx);
-    RootedShape newShape(cx, EmptyShape::getInitialShape(cx, res->getClass(),
-                                                         res->getTaggedProto(),
-                                                         res->getMetadata(),
-                                                         res->getParent(),
-                                                         res->numFixedSlots(),
-                                                         shape->getObjectFlags()));
+    RootedShape newShape(cx, res->lastProperty());
     for (unsigned i = 0; i < ids.length(); i++) {
         id = ids[i];
         MOZ_ASSERT(!res->contains(cx, id));
 
         uint32_t index;
         bool indexed = js_IdIsIndex(id, &index);
 
         Rooted<UnownedBaseShape*> nbase(cx, newShape->base()->unowned());