diff --git a/typo3/sysext/backend/Classes/Controller/SiteSettingsController.php b/typo3/sysext/backend/Classes/Controller/SiteSettingsController.php
index 778c1165f0035261f712fde02be3074ad82f7073..8027cb6d57196f8038e538f689f3b2342dfd8aed 100644
--- a/typo3/sysext/backend/Classes/Controller/SiteSettingsController.php
+++ b/typo3/sysext/backend/Classes/Controller/SiteSettingsController.php
@@ -179,7 +179,7 @@ readonly class SiteSettingsController
         $parsedBody = $request->getParsedBody();
 
         $returnUrl = GeneralUtility::sanitizeLocalUrl(
-            (string)($parsedBody['returnUrl'])
+            (string)($parsedBody['returnUrl'] ?? '')
         ) ?: null;
         $overviewUrl = $this->uriBuilder->buildUriFromRoute('site_settings');
         $CMD = $parsedBody['CMD'] ?? '';