diff --git a/test/Integration/AbstractIntegrationTestCase.php b/test/Integration/AbstractIntegrationTestCase.php
index fdfc6f6..f714465 100644
--- a/test/Integration/AbstractIntegrationTestCase.php
+++ b/test/Integration/AbstractIntegrationTestCase.php
@@ -90,7 +90,7 @@ protected function assertPgAdvisoryLocksCount(
     private function findPostgresAdvisoryLockInConnection(
         PDO $dbConnection,
         PostgresLockId $postgresLockId,
-    ): ?object {
+    ): object | null {
         $id = $postgresLockId->id;
 
         $lockObjectId = $id % self::POSTGRES_BLOCK_SIZE;