diff --git a/app/assets/javascripts/discourse/controllers/topic.js.es6 b/app/assets/javascripts/discourse/controllers/topic.js.es6
index 11f4fe4cba1..9a464c463cf 100644
--- a/app/assets/javascripts/discourse/controllers/topic.js.es6
+++ b/app/assets/javascripts/discourse/controllers/topic.js.es6
@@ -14,7 +14,7 @@ import { popupAjaxError } from 'discourse/lib/ajax-error';
 import { spinnerHTML } from 'discourse/helpers/loading-spinner';
 import { userPath } from 'discourse/lib/url';
 
-const customPostMessageCallbacks = {};
+let customPostMessageCallbacks = {};
 
 export function resetCustomPostMessageCallbacks() {
   customPostMessageCallbacks = {};