diff --git a/js/src/jsinterp.cpp b/js/src/jsinterp.cpp
index ae5d75d6f94e..62141b5ada71 100644
--- a/js/src/jsinterp.cpp
+++ b/js/src/jsinterp.cpp
@@ -231,7 +231,8 @@ js_FillPropertyCache(JSContext *cx, JSObject *obj, jsuword kshape,
 #endif
                         SCOPE_MAKE_UNIQUE_SHAPE(cx, scope);
                         SCOPE_SET_BRANDED(scope);
-                        kshape = scope->shape;
+                        if (OBJ_SCOPE(obj) == scope)
+                            kshape = scope->shape;
                     }
                     vword = JSVAL_OBJECT_TO_PCVAL(v);
                     break;