diff --git a/calendar/inc/class.calendar_groupdav.inc.php b/calendar/inc/class.calendar_groupdav.inc.php
index 49d188498a..7354ba1254 100644
--- a/calendar/inc/class.calendar_groupdav.inc.php
+++ b/calendar/inc/class.calendar_groupdav.inc.php
@@ -954,10 +954,6 @@ class calendar_groupdav extends Api\CalDAV\Handler
 			}
 			// if no edit-rights (aka no organizer), update only attendee stuff: status and alarms
 			if (!$this->check_access(Acl::EDIT, $oldEvent) ||
-				// Work around problems with Outlook CalDAV Synchroniser (https://caldavsynchronizer.org/)
-				// - always sends all participants back with status NEEDS-ACTION --> resets status of all participant, if user has edit rights
-				// --> allow full updates only for organizer
-				self::get_agent() == 'caldavsynchronizer' && $oldEvent['owner'] != $user ||
 				// we ignored Lightings If-None-Match: "*" --> do not overwrite event, just change status
 				!empty($workaround_lightning_if_none_match))
 			{
diff --git a/calendar/inc/class.calendar_ical.inc.php b/calendar/inc/class.calendar_ical.inc.php
index e0dfec10cb..cdf64b182c 100644
--- a/calendar/inc/class.calendar_ical.inc.php
+++ b/calendar/inc/class.calendar_ical.inc.php
@@ -1308,7 +1308,10 @@ class calendar_ical extends calendar_boupdate
 					// if the client does not return a status, we restore the original one
 					foreach ($event['participants'] as $uid => $status)
 					{
-						if ($status[0] == 'X')
+						// Work around problems with Outlook CalDAV Synchronizer (https://caldavsynchronizer.org/)
+						// - always sends all participants back with status NEEDS-ACTION --> resets status of all participant, if user has edit rights
+						// --> allow only updates with other status then NEEDS-ACTION and therefore allow accepting or denying meeting requests for the user himself
+						if ($status[0] === 'X' || calendar_groupdav::get_agent() === 'caldavsynchronizer' && $status[0] === 'U')
 						{
 							if (isset($event_info['stored_event']['participants'][$uid]))
 							{