diff --git a/Classes/Authentication/HttpBackendUserAuthentication.php b/Classes/Authentication/HttpBackendUserAuthentication.php
index 23651872..35cbd264 100644
--- a/Classes/Authentication/HttpBackendUserAuthentication.php
+++ b/Classes/Authentication/HttpBackendUserAuthentication.php
@@ -115,6 +115,10 @@ protected function authenticateBearerToken(ServerRequestInterface $request): voi
 
         [$scheme, $token] = GeneralUtility::trimExplode(' ', $authorizationHeader, true);
 
+        if ($scheme === null) {
+            return;
+        }
+
         if (is_string($scheme) && strtolower($scheme) !== 'bearer') {
             return;
         }