diff --git a/lib/AppInfo/Application.php b/lib/AppInfo/Application.php
index 4f060eabf2a33ed789cddd912d79ac75e75e06f7..3b90a6d99b4f1f850f5f6951d44c3105811fc58a 100644
--- a/lib/AppInfo/Application.php
+++ b/lib/AppInfo/Application.php
@@ -16,6 +16,7 @@ use OCA\Calendar\Middleware\InvitationMiddleware;
 use OCA\Calendar\Notification\Notifier;
 use OCA\Calendar\Profile\AppointmentsAction;
 use OCA\Calendar\Reference\ReferenceProvider;
+use OCA\DAV\Connector\Sabre\Principal;
 use OCP\AppFramework\App;
 use OCP\AppFramework\Bootstrap\IBootContext;
 use OCP\AppFramework\Bootstrap\IBootstrap;
@@ -65,6 +66,7 @@ class Application extends App implements IBootstrap {
 				$c->get(LoggerInterface::class),
 				$c->get(IUserManager::class),
 				$c->get(L10NFactory::class),
+				$c->get(Principal::class),
 			);
 		});
 
@@ -89,6 +91,7 @@ class Application extends App implements IBootstrap {
 				$c->get(LoggerInterface::class),
 				$c->get(IUserManager::class),
 				$c->get(L10NFactory::class),
+				$c->get(Principal::class),
 			);
 		});
 
diff --git a/lib/Middleware/InvitationMiddleware.php b/lib/Middleware/InvitationMiddleware.php
index 2c2027fa36b04aa0ff83a560308ed1487a994c2e..1aedaeab7de2ae58d281319469d0dfdaf53df893 100644
--- a/lib/Middleware/InvitationMiddleware.php
+++ b/lib/Middleware/InvitationMiddleware.php
@@ -3,6 +3,7 @@
 namespace OCA\Calendar\Middleware;
 
 use OCA\Calendar\Controller\InvitationMaybeController;
+use OCA\DAV\Connector\Sabre\Principal;
 use OCA\Dav\Controller\InvitationResponseController;
 use OCP\AppFramework\Http\Response;
 use OCP\AppFramework\Middleware;
@@ -34,6 +35,7 @@ class InvitationMiddleware extends Middleware {
 		LoggerInterface $logger,
 		IUserManager $iusermanager,
 		IFactory $languageFactory,
+		private Principal $principalBackend,
 	) {
 		$this->request = $request;
 		$this->config = $config;
@@ -75,17 +77,27 @@ class InvitationMiddleware extends Middleware {
 
 			$uid = $row['uid'];
 			$sender = substr($row['attendee'], 7);
-			$recipient = substr($row['organizer'], 7);
-
+			
+			$organizer = $row['organizer'];
+			$recipient = substr($organizer, 7);
+			
+			$principalUriOfOrganizer = $this->principalBackend->findByUri($organizer, 'principals/users');
+			if ($principalUriOfOrganizer === null) {
+				$this->logger->warning('Principal URI not found for organizer', ['organizer' => $organizer]);
+				return $response;
+			}
+			
 			$query2 = $this->db->getQueryBuilder();
 			$query2
-				->select('*')
-				->from('calendarobjects')
+				->select('co.*')
+				->from('calendarobjects', 'co')
+				->join('co', 'calendars', 'c', $query2->expr()->eq('co.calendarid', 'c.id'))
 				->where(
-					$query
+					$query2
 						->expr()
 						->eq('uid', $query2->createNamedParameter($uid))
-				);
+				)->andWhere($query2->expr()->eq('c.principaluri', $query2->createNamedParameter($principalUriOfOrganizer)));
+	
 			$stmt2 = $query2->execute();
 			$row2 = $stmt2->fetch(\PDO::FETCH_ASSOC);
 			$calendarobjectid = $row2['id'];
@@ -150,6 +162,8 @@ class InvitationMiddleware extends Middleware {
 				$organizername = $recipient;
 			}
 
+			$defaultVal = '';
+
 			if ($methodName === 'tentative') {
 				$meetingTitle = $this->l10n->t('Invitation Tentatively Accepted: %s', [$SUMMARY]);