diff --git a/apps/dav/lib/CalDAV/Reminder/Notifier.php b/apps/dav/lib/CalDAV/Reminder/Notifier.php
index 7618222f42a5a..310f5e5b23ddc 100644
--- a/apps/dav/lib/CalDAV/Reminder/Notifier.php
+++ b/apps/dav/lib/CalDAV/Reminder/Notifier.php
@@ -36,6 +36,7 @@
 use OCP\IL10N;
 use OCP\IURLGenerator;
 use OCP\L10N\IFactory;
+use OCP\Notification\AlreadyProcessedException;
 use OCP\Notification\INotification;
 use OCP\Notification\INotifier;
 
@@ -223,6 +224,12 @@ private function getTitleFromParameters(array $parameters):string {
 	private function generateDateString(array $parameters):string {
 		$startDateTime = DateTime::createFromFormat(\DateTime::ATOM, $parameters['start_atom']);
 		$endDateTime = DateTime::createFromFormat(\DateTime::ATOM, $parameters['end_atom']);
+
+		// If the event has already ended, dismiss the notification
+		if ($endDateTime < $this->timeFactory->getDateTime()) {
+			throw new AlreadyProcessedException();
+		}
+
 		$isAllDay = $parameters['all_day'];
 		$diff = $startDateTime->diff($endDateTime);
 
diff --git a/apps/dav/tests/unit/CalDAV/Reminder/NotifierTest.php b/apps/dav/tests/unit/CalDAV/Reminder/NotifierTest.php
index b4f5d7dea9eab..43741f24b38f6 100644
--- a/apps/dav/tests/unit/CalDAV/Reminder/NotifierTest.php
+++ b/apps/dav/tests/unit/CalDAV/Reminder/NotifierTest.php
@@ -36,23 +36,25 @@
 use OCP\IL10N;
 use OCP\IURLGenerator;
 use OCP\L10N\IFactory;
+use OCP\Notification\AlreadyProcessedException;
 use OCP\Notification\INotification;
+use PHPUnit\Framework\MockObject\MockObject;
 use Test\TestCase;
 
 class NotifierTest extends TestCase {
 	/** @var Notifier */
 	protected $notifier;
 
-	/** @var IFactory|\PHPUnit\Framework\MockObject\MockObject */
+	/** @var IFactory|MockObject */
 	protected $factory;
 
-	/** @var IURLGenerator|\PHPUnit\Framework\MockObject\MockObject */
+	/** @var IURLGenerator|MockObject */
 	protected $urlGenerator;
 
-	/** @var IL10N|\PHPUnit\Framework\MockObject\MockObject */
+	/** @var IL10N|MockObject */
 	protected $l10n;
 
-	/** @var ITimeFactory|\PHPUnit\Framework\MockObject\MockObject */
+	/** @var ITimeFactory|MockObject */
 	protected $timeFactory;
 
 	protected function setUp(): void {
@@ -111,7 +113,7 @@ public function testPrepareWrongApp(): void {
 		$this->expectException(\InvalidArgumentException::class);
 		$this->expectExceptionMessage('Notification not from this app');
 
-		/** @var INotification|\PHPUnit\Framework\MockObject\MockObject $notification */
+		/** @var INotification|MockObject $notification */
 		$notification = $this->createMock(INotification::class);
 
 		$notification->expects($this->once())
@@ -128,7 +130,7 @@ public function testPrepareWrongSubject() {
 		$this->expectException(\InvalidArgumentException::class);
 		$this->expectExceptionMessage('Unknown subject');
 
-		/** @var INotification|\PHPUnit\Framework\MockObject\MockObject $notification */
+		/** @var INotification|MockObject $notification */
 		$notification = $this->createMock(INotification::class);
 
 		$notification->expects($this->once())
@@ -165,6 +167,28 @@ public function dataPrepare(): array {
 				],
 				"Calendar: Personal\r\nDate: 2005-08-15T15:52:01+02:00, 2005-08-15T15:52:01+02:00 - 2005-08-15T17:52:01+02:00 (Europe/Berlin)\r\nWhere: NC Headquarters"
 			],
+			[
+				'calendar_reminder',
+				[
+					'title' => 'Title of this event',
+					'start_atom' => '2005-08-15T13:00:00+02:00',
+				],
+				'Title of this event (1 hour ago)',
+				[
+					'title' => 'Title of this event',
+					'description' => null,
+					'location' => 'NC Headquarters',
+					'all_day' => false,
+					'start_atom' => '2005-08-15T13:00:00+02:00',
+					'start_is_floating' => false,
+					'start_timezone' => 'Europe/Berlin',
+					'end_atom' => '2005-08-15T15:00:00+02:00',
+					'end_is_floating' => false,
+					'end_timezone' => 'Europe/Berlin',
+					'calendar_displayname' => 'Personal',
+				],
+				"Calendar: Personal\r\nDate: 2005-08-15T13:00:00+02:00, 2005-08-15T13:00:00+02:00 - 2005-08-15T15:00:00+02:00 (Europe/Berlin)\r\nWhere: NC Headquarters"
+			],
 		];
 	}
 
@@ -179,7 +203,7 @@ public function dataPrepare(): array {
 	 * @throws \Exception
 	 */
 	public function testPrepare(string $subjectType, array $subjectParams, string $subject, array $messageParams, string $message): void {
-		/** @var INotification|\PHPUnit\Framework\MockObject\MockObject $notification */
+		/** @var INotification|MockObject $notification */
 		$notification = $this->createMock(INotification::class);
 
 		$notification->expects($this->once())
@@ -222,4 +246,49 @@ public function testPrepare(string $subjectType, array $subjectParams, string $s
 
 		$this->assertEquals($notification, $return);
 	}
+
+	public function testPassedEvent(): void {
+		/** @var INotification|MockObject $notification */
+		$notification = $this->createMock(INotification::class);
+
+		$notification->expects($this->once())
+			->method('getApp')
+			->willReturn(Application::APP_ID);
+		$notification->expects($this->once())
+			->method('getSubject')
+			->willReturn('calendar_reminder');
+		$notification->expects($this->once())
+			->method('getSubjectParameters')
+			->willReturn([
+				'title' => 'Title of this event',
+				'start_atom' => '2005-08-15T08:00:00+02:00'
+			]);
+
+		$notification->expects($this->once())
+			->method('getMessageParameters')
+			->willReturn([
+				'title' => 'Title of this event',
+				'description' => null,
+				'location' => 'NC Headquarters',
+				'all_day' => false,
+				'start_atom' => '2005-08-15T08:00:00+02:00',
+				'start_is_floating' => false,
+				'start_timezone' => 'Europe/Berlin',
+				'end_atom' => '2005-08-15T13:00:00+02:00',
+				'end_is_floating' => false,
+				'end_timezone' => 'Europe/Berlin',
+				'calendar_displayname' => 'Personal',
+			]);
+
+		$notification->expects($this->once())
+			->method('setParsedSubject')
+			->with('Title of this event (6 hours ago)')
+			->willReturnSelf();
+
+		$this->expectException(AlreadyProcessedException::class);
+
+		$return = $this->notifier->prepare($notification, 'en');
+
+		$this->assertEquals($notification, $return);
+	}
 }