--- a/js/src/xpconnect/src/xpccomponents.cpp
+++ b/js/src/xpconnect/src/xpccomponents.cpp
@@ -3232,20 +3232,19 @@ xpc_CreateSandboxObject(JSContext * cx, 
             return NS_ERROR_XPC_UNEXPECTED;
 
         if (proto) {
             bool ok = JS_WrapObject(cx, &proto);
             if (!ok)
                 return NS_ERROR_XPC_UNEXPECTED;
 
             if (xpc::WrapperFactory::IsXrayWrapper(proto) && !wantXrays) {
-                jsval v;
-                if (!JS_GetProperty(cx, proto, "wrappedJSObject", &v))
-                    return NS_ERROR_XPC_UNEXPECTED;
-
+                jsval v = OBJECT_TO_JSVAL(proto);
+                if (!xpc::WrapperFactory::WaiveXrayAndWrap(cx, &v))
+                    return NS_ERROR_FAILURE;
                 proto = JSVAL_TO_OBJECT(v);
             }
 
             ok = JS_SetPrototype(cx, sandbox, proto);
             if (!ok)
                 return NS_ERROR_XPC_UNEXPECTED;
         }