diff --git a/Classes/Controller/BackendServiceController.php b/Classes/Controller/BackendServiceController.php
index 816eab2273..adc388d582 100644
--- a/Classes/Controller/BackendServiceController.php
+++ b/Classes/Controller/BackendServiceController.php
@@ -585,7 +585,7 @@ public function flowQueryAction(array $chain): string
         }
 
         /** @see GetOperation */
-        assert(is_callable([$flowQuery, 'get']));
+        assert(is_object($flowQuery) && is_callable([$flowQuery, 'get']));
 
         $nodeInfoHelper = new NodeInfoHelper();
         $type = $finisher['type'] ?? null;