diff --git a/plugins/kolab_files/kolab_files.js b/plugins/kolab_files/kolab_files.js
index 67e06686..a2959539 100644
--- a/plugins/kolab_files/kolab_files.js
+++ b/plugins/kolab_files/kolab_files.js
@@ -1306,7 +1306,7 @@ function document_editor_close()
     .dialog({
       resizable: false,
       closeOnEscape: true,
-      dialogClass: 'popupmessage error',
+      dialogClass: 'error',
       title: rcmail.gettext('kolab_files.sessionterminatedtitle'),
       close: function() { window.close(); },
       width: 420,