diff --git a/calendar/inc/class.calendar_boupdate.inc.php b/calendar/inc/class.calendar_boupdate.inc.php
index a74a6d80a9..630f307e61 100644
--- a/calendar/inc/class.calendar_boupdate.inc.php
+++ b/calendar/inc/class.calendar_boupdate.inc.php
@@ -1570,6 +1570,13 @@ class calendar_boupdate extends calendar_bo
 			// we convert here from user-time to timestamps in server-time!
 			if (isset($save_event[$ts])) $save_event[$ts] = $save_event[$ts] ? calendar_bo::date2ts($save_event[$ts], true) : 0;
 		}
+		foreach(['start','end','recur_enddate'] as $ts)
+		{
+			if(is_object($save_event[$ts]))
+			{
+				$save_event[$ts] = $save_event[$ts]->format('ts');
+			}
+		}
 		$tracking->track($save_event, $old_event);
 
 		return $cal_id;