diff --git a/js/src/jsexn.c b/js/src/jsexn.c
index 9e0d7f6dfb3..2f6cf70fef8 100644
--- a/js/src/jsexn.c
+++ b/js/src/jsexn.c
@@ -1052,8 +1052,7 @@ js_InitExceptionClasses(JSContext *cx, JSObject *obj)
 
         /* Make a constructor function for the current name. */
         atom = cx->runtime->atomState.classAtoms[exceptions[i].key];
-        fun = js_DefineFunction(cx, obj, atom, exceptions[i].native, 3,
-                                JSPROP_READONLY | JSPROP_PERMANENT);
+        fun = js_DefineFunction(cx, obj, atom, exceptions[i].native, 3, 0);
         if (!fun)
             break;