diff --git a/apps/dav/lib/CalDAV/CalDavBackend.php b/apps/dav/lib/CalDAV/CalDavBackend.php
index b6ec6ad2c18f5..b3d16b28a4057 100644
--- a/apps/dav/lib/CalDAV/CalDavBackend.php
+++ b/apps/dav/lib/CalDAV/CalDavBackend.php
@@ -3008,7 +3008,7 @@ public function getDenormalizedData(string $calendarData): array {
 		// VTODO components can have no start date
 		/** @var  */
 		$startDate = $component->DTSTART instanceof \Sabre\VObject\Property\ICalendar\DateTime ? $component->DTSTART->getDateTime() : null;
-		$endDate = clone $startDate;
+		$endDate = $startDate ? clone $startDate : null;
 		if ($startDate) {
 			// Recurring
 			if ($component->RRULE || $component->RDATE) {