diff --git a/src/Controller/ErrorController.php b/src/Controller/ErrorController.php
index 34543fb9d..25f625da1 100644
--- a/src/Controller/ErrorController.php
+++ b/src/Controller/ErrorController.php
@@ -178,7 +178,7 @@ private function isMaintenanceEnabled(int $code): bool
             return false;
         }
 
-        return $this->config->get('general/maintenance_mode', false);
+        return filter_var($this->config->get('general/maintenance_mode', false), FILTER_VALIDATE_BOOLEAN);
     }
 
     private function attemptToRender(string $item): ?Response