diff --git a/data/class/pages/frontparts/bloc/LC_Page_FrontParts_Bloc_Calendar.php b/data/class/pages/frontparts/bloc/LC_Page_FrontParts_Bloc_Calendar.php
index 644f0a76d1..3e9418233f 100644
--- a/data/class/pages/frontparts/bloc/LC_Page_FrontParts_Bloc_Calendar.php
+++ b/data/class/pages/frontparts/bloc/LC_Page_FrontParts_Bloc_Calendar.php
@@ -21,7 +21,7 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  */
 
-define('CALENDAR_ROOT', DATA_REALDIR.'module/Calendar'.DIRECTORY_SEPARATOR);
+defined('CALENDAR_ROOT') or define('CALENDAR_ROOT', DATA_REALDIR.'module/Calendar'.DIRECTORY_SEPARATOR);
 require_once CLASS_EX_REALDIR . 'page_extends/frontparts/bloc/LC_Page_FrontParts_Bloc_Ex.php';
 
 /**