diff --git a/js/src/jsfun.cpp b/js/src/jsfun.cpp
index 704a8d7af6aa..66ec82e91f01 100644
--- a/js/src/jsfun.cpp
+++ b/js/src/jsfun.cpp
@@ -2482,6 +2482,7 @@ js_CloneFunctionObject(JSContext *cx, JSFunction *fun, JSObject *parent,
             JS_ASSERT(script->compartment != cx->compartment);
             JS_OPT_ASSERT(script->ownerObject == fun);
 
+            cfun->u.i.script = NULL;
             JSScript *cscript = js_CloneScript(cx, script);
             if (!cscript)
                 return NULL;