diff --git a/classes/calendar_helpers.php b/classes/calendar_helpers.php
index e4e3f93..dc0e0f2 100644
--- a/classes/calendar_helpers.php
+++ b/classes/calendar_helpers.php
@@ -84,7 +84,7 @@ function attendance_create_calendar_events($sessionsids) {
  * @param $timestart int start time of the event
  * @return bool result of updating
  */
-function attendance_update_calendar_event($caleventid, $timeduration, $timestart = null) {
+function attendance_update_calendar_event($caleventid, $timeduration, $timestart) {
     $caleventdata = new stdClass();
     $caleventdata->timeduration   = $timeduration;
     $caleventdata->timestart      = $timestart;
diff --git a/classes/structure.php b/classes/structure.php
index c8d657c..772a021 100644
--- a/classes/structure.php
+++ b/classes/structure.php
@@ -919,7 +919,7 @@ class mod_attendance_structure {
             $sess->timemodified = $now;
             $DB->update_record('attendance_sessions', $sess);
             if ($sess->caleventid) {
-                attendance_update_calendar_event($sess->caleventid, $duration);
+                attendance_update_calendar_event($sess->caleventid, $duration, $sess->sessdate);
             }
             $event = \mod_attendance\event\session_duration_updated::create(array(
                 'objectid' => $this->id,