diff --git a/apps/dav/lib/CalDAV/CalDavBackend.php b/apps/dav/lib/CalDAV/CalDavBackend.php
index 51eb505124e38..b60d731b21512 100644
--- a/apps/dav/lib/CalDAV/CalDavBackend.php
+++ b/apps/dav/lib/CalDAV/CalDavBackend.php
@@ -658,7 +658,7 @@ public function getCalendarByUri($principal, $uri) {
 	}
 
 	/**
-	 * @return array{id: int, uri: string, '{http://calendarserver.org/ns/}getctag': string, '{http://sabredav.org/ns}sync-token': int, '{urn:ietf:params:xml:ns:caldav}supported-calendar-component-set': SupportedCalendarComponentSet, '{urn:ietf:params:xml:ns:caldav}schedule-calendar-transp': ScheduleCalendarTransp }|null
+	 * @return array{id: int, uri: string, '{http://calendarserver.org/ns/}getctag': string, '{http://sabredav.org/ns}sync-token': int, '{urn:ietf:params:xml:ns:caldav}supported-calendar-component-set': SupportedCalendarComponentSet, '{urn:ietf:params:xml:ns:caldav}schedule-calendar-transp': ScheduleCalendarTransp, '{urn:ietf:params:xml:ns:caldav}calendar-timezone': ?string }|null
 	 */
 	public function getCalendarById(int $calendarId): ?array {
 		$fields = array_column($this->propertyMap, 0);
diff --git a/apps/dav/lib/CalDAV/Reminder/ReminderService.php b/apps/dav/lib/CalDAV/Reminder/ReminderService.php
index 9eff737816b45..3ed689ad3fe9a 100644
--- a/apps/dav/lib/CalDAV/Reminder/ReminderService.php
+++ b/apps/dav/lib/CalDAV/Reminder/ReminderService.php
@@ -308,7 +308,7 @@ public function onCalendarObjectCreate(array $objectData):void {
 
 					try {
 						$triggerTime = $valarm->getEffectiveTriggerTime();
-						if (!$triggerTime->getTimezone() || $triggerTime->getTimezone()->getName() === 'UTC') {
+						if ($triggerTime->getTimezone() === false || $triggerTime->getTimezone()->getName() === 'UTC') {
 							$triggerTime = new DateTimeImmutable(
 								$triggerTime->format('Y-m-d H:i:s'),
 								$calendarTimeZone
@@ -396,7 +396,7 @@ private function getRemindersForVAlarm(VAlarm $valarm,
 		$isRelative = $this->isAlarmRelative($valarm);
 		/** @var DateTimeImmutable $notificationDate */
 		$notificationDate = $valarm->getEffectiveTriggerTime();
-		if (!$notificationDate->getTimezone() || $notificationDate->getTimezone()->getName() === 'UTC') {
+		if ($notificationDate->getTimezone() === false || $notificationDate->getTimezone()->getName() === 'UTC') {
 			$notificationDate = new DateTimeImmutable(
 				$notificationDate->format('Y-m-d H:i:s'),
 				$calendarTimeZone
@@ -857,7 +857,10 @@ private function getCalendarTimeZone(int $calendarid): DateTimeZone {
 		}
 		// This property contains a VCALENDAR with a single
 		// VTIMEZONE.
+		/** @var VObject\Component\VCalendar $vtimezoneObj */
 		$vtimezoneObj = VObject\Reader::read($calendarInfo[$tzProp]);
-		return $vtimezoneObj->VTIMEZONE->getTimeZone();
+		/** @var VObject\Component\VTimeZone $vtimezone */
+		$vtimezone = $vtimezoneObj->VTIMEZONE;
+		return $vtimezone->getTimeZone();
 	}
 }