diff --git a/html/ajax_listports.php b/html/ajax_listports.php
index b9245ebe3..d3c5937e1 100755
--- a/html/ajax_listports.php
+++ b/html/ajax_listports.php
@@ -12,7 +12,7 @@
  *
  */
 
-if ($_GET['debug'])
+if (isset($_GET['debug']))
 {
   ini_set('display_errors', 1);
   ini_set('display_startup_errors', 0);