diff --git a/calendar/inc/class.calendar_uiforms.inc.php b/calendar/inc/class.calendar_uiforms.inc.php
index 12ec2e576c..6d3102eb3c 100644
--- a/calendar/inc/class.calendar_uiforms.inc.php
+++ b/calendar/inc/class.calendar_uiforms.inc.php
@@ -2428,7 +2428,7 @@ class calendar_uiforms extends calendar_ui
 		}
 		$tpl = new Etemplate('calendar.meeting');
 		$tpl->exec('calendar.calendar_uiforms.meeting', $event, array(), $readonlys, $event+array(
-			'old' => $existing_event ?: [],
+			'old' => is_array($existing_event) ? $existing_event : [],
 			'extern_organizer' => $extern_organizer ?? [],
 			'from_extern_organizer' => $from_extern_organizer ?? false,
 		), 2);