diff --git a/app/assets/javascripts/discourse/initializers/subscribe-user-notifications.js.es6 b/app/assets/javascripts/discourse/initializers/subscribe-user-notifications.js.es6
index 0dd8250fe44..96ea1ef8d01 100644
--- a/app/assets/javascripts/discourse/initializers/subscribe-user-notifications.js.es6
+++ b/app/assets/javascripts/discourse/initializers/subscribe-user-notifications.js.es6
@@ -114,8 +114,8 @@ export default {
       const router = container.lookup("router:main");
 
       bus.subscribe("/categories", data => {
-        data.categories.forEach(c => site.updateCategory(c));
-        data.deleted_categories.forEach(id => site.removeCategory(id));
+        (data.categories || []).forEach(c => site.updateCategory(c));
+        (data.deleted_categories || []).forEach(id => site.removeCategory(id));
       });
 
       bus.subscribe("/client_settings", data =>