diff --git a/public_html/includes/class/class.LSsession.php b/public_html/includes/class/class.LSsession.php
index f188f7b9..ee74eb67 100644
--- a/public_html/includes/class/class.LSsession.php
+++ b/public_html/includes/class/class.LSsession.php
@@ -574,7 +574,7 @@ class LSsession {
       if (self :: LSldapConnect()) {
 
         // topDn
-        if ( $_POST['LSsession_topDn'] != '' ){
+        if (isset($_POST['LSsession_topDn']) && $_POST['LSsession_topDn'] != '' ){
           self :: $topDn = $_POST['LSsession_topDn'];
         }
         else {