--- a/js/DataTables/Plugins/editor.select2.js
+++ b/js/DataTables/Plugins/editor.select2.js
@@ -207,6 +207,12 @@ _fieldTypes.select2 = {
         }
  
         if ( needAjax ) {
+            // beforeSend() is using plain-text value of the 'url' parameter.
+            // We have to determine the actual value of the 'url' themselves.
+            var url = (typeof conf.opts.ajax.url === 'function')
+                ? conf.opts.ajax.url.call()
+                : conf.opts.ajax.url;
+
             $.ajax( $.extend( {
                 beforeSend: function ( jqXhr, settings ) {
                     // Add an initial data request to the server, but don't
@@ -215,9 +221,10 @@ _fieldTypes.select2 = {
                         JSON.stringify(val);
 
                     if ( settings.type === 'GET' ) {
-                        settings.url += settings.url.indexOf('?') === -1 ?
+                        url += url.indexOf('?') === -1 ?
                             '?'+initData :
                             '&'+initData;
+                        settings.url = url;
                     }
                     else {
                         settings.data = settings.data ?