diff --git a/js/src/vm/RegExpObject.cpp b/js/src/vm/RegExpObject.cpp
index c00ac5658b7..f52e9a0d7e8 100644
--- a/js/src/vm/RegExpObject.cpp
+++ b/js/src/vm/RegExpObject.cpp
@@ -795,7 +795,7 @@ js::CloneRegExpObject(JSContext *cx, JSObject *obj_)
     RegExpObjectBuilder builder(cx);
     Rooted<RegExpObject*> regex(cx, &obj_->as<RegExpObject>());
     JSObject *res = builder.clone(regex);
-    JS_ASSERT(res->type() == regex->type());
+    JS_ASSERT_IF(res, res->type() == regex->type());
     return res;
 }