diff --git a/public/typo3conf/ext/ep_theme/Classes/Middleware/ReferrerMiddleware.php b/public/typo3conf/ext/ep_theme/Classes/Middleware/ReferrerMiddleware.php
index 35eed7a5..b5a98570 100644
--- a/public/typo3conf/ext/ep_theme/Classes/Middleware/ReferrerMiddleware.php
+++ b/public/typo3conf/ext/ep_theme/Classes/Middleware/ReferrerMiddleware.php
@@ -22,6 +22,10 @@ class ReferrerMiddleware implements MiddlewareInterface
 
         $ref = $queryParams['ref'];
 
+        if (false === is_numeric($ref)) {
+            return $handler->handle($request);
+        }
+
         /** @var SiteFinder $siteFinder */
         $siteFinder = GeneralUtility::makeInstance(SiteFinder::class);