diff --git a/calendar/inc/class.calendar_boupdate.inc.php b/calendar/inc/class.calendar_boupdate.inc.php
index 0d7efbde1e..5b0d503005 100644
--- a/calendar/inc/class.calendar_boupdate.inc.php
+++ b/calendar/inc/class.calendar_boupdate.inc.php
@@ -1591,7 +1591,7 @@ class calendar_boupdate extends calendar_bo
 				$save_event[$ts] = $save_event[$ts]->format('ts');
 			}
 		}
-		$tracking->track($save_event, $old_event);
+		$tracking->track($save_event, $old_event ?: null);
 
 		return $cal_id;
 	}
@@ -1832,7 +1832,7 @@ class calendar_boupdate extends calendar_bo
 			if (($event = $this->read($cal_id, $recur_date, $ignore_acl, 'server')))
 			{
 				$tracking = new calendar_tracking($this);
-				$tracking->track($event, $old_event);
+				$tracking->track($event, $old_event ?: null);
 			}
 			// notify the link-class about the update, as other apps may be subscribed to it
 			Link::notify_update('calendar', $cal_id, $event, "update");