diff --git a/lib/NotificationGenerator.php b/lib/NotificationGenerator.php
index 99e3e3b70..367cbc16b 100644
--- a/lib/NotificationGenerator.php
+++ b/lib/NotificationGenerator.php
@@ -118,7 +118,12 @@ public function prepare(INotification $notification, string $languageCode): INot
 		$event = $this->populateEvent($event, $languageCode);
 		$this->activityManager->setCurrentUserId(null);
 
-		return $this->getDisplayNotificationForEvent($event, $event->getObjectId());
+		try {
+			return $this->getDisplayNotificationForEvent($event, $event->getObjectId());
+		} catch (\InvalidArgumentException $e) {
+			$this->logger->error('Failed to format activity notification', ['exception' => $e]);
+			throw new AlreadyProcessedException();
+		}
 	}
 
 	private function getDisplayNotificationForEvent(IEvent $event, int $activityId): INotification {