diff --git a/js/functions.js b/js/functions.js
index b449070b5b6e..35bc54b038b1 100644
--- a/js/functions.js
+++ b/js/functions.js
@@ -5093,9 +5093,8 @@ function configGet(key, cached=true)
 jQuery.fn.getPostData = function() {
     var dataPost = this.attr('data-post');
     // Strip possible leading ?
-    if (dataPost.startsWith('?')) {
+    if (dataPost !== undefined && dataPost.startsWith('?')) {
         dataPost = dataPost.substr(1);
     }
     return dataPost;
 };
-