diff --git a/Classes/Service/StyleguideConfigurationManager.php b/Classes/Service/StyleguideConfigurationManager.php
index 76e679d..fdd7a8c 100644
--- a/Classes/Service/StyleguideConfigurationManager.php
+++ b/Classes/Service/StyleguideConfigurationManager.php
@@ -269,7 +269,7 @@ protected function generateAssetUrl(string $path): Uri
                 PathUtility::getAbsoluteWebPath($path, false)
             )
             ->withQuery('?' . $modified)
-            ->withPort(GeneralUtility::getIndpEnv('TYPO3_PORT') ?: null);
+            ->withPort((int) GeneralUtility::getIndpEnv('TYPO3_PORT') ?: null);
     }
 
     /**