diff --git a/popuphelp.php b/popuphelp.php
index be2bc58323..03be21eaff 100644
--- a/popuphelp.php
+++ b/popuphelp.php
@@ -19,7 +19,7 @@
 // +-----------------------------------------------------------------------+
 check_status(ACCESS_GUEST);
 
-echo $_GET['asdf'];
+if (isset($_GET['asdf'])) echo htmlspecialchars($_GET['asdf'], ENT_QUOTES, 'UTF-8');
 
 $page['body_id'] = 'thePopuphelpPage';
 $title = l10n('Piwigo Help');