diff --git a/calendar/inc/class.calendar_export_ical.inc.php b/calendar/inc/class.calendar_export_ical.inc.php
index f2d69bcd8c..621596de0d 100644
--- a/calendar/inc/class.calendar_export_ical.inc.php
+++ b/calendar/inc/class.calendar_export_ical.inc.php
@@ -38,7 +38,7 @@ class calendar_export_ical extends calendar_export_csv {
 		{
 			$query = array(
 				'start' => $options['criteria']['start'],
-				'end'   => strtotime('+1 day',$options['criteria']['end'])-1,
+				'end'   => $options['criteria']['end'] ? strtotime('+1 day',$options['criteria']['end'])-1 : null,
 				'categories'	=> $options['categories'],
 				'daywise'       => false,
 				'users'         => $options['criteria']['owner'],