diff --git a/typo3/sysext/core/Classes/Routing/SiteMatcher.php b/typo3/sysext/core/Classes/Routing/SiteMatcher.php
index c8f298249e3ae48d04b3c4839d5ed6aa483b7e85..137c4ab75c727acf0fcdf8cbaab62853e371cd73 100644
--- a/typo3/sysext/core/Classes/Routing/SiteMatcher.php
+++ b/typo3/sysext/core/Classes/Routing/SiteMatcher.php
@@ -245,7 +245,7 @@ class SiteMatcher implements SingletonInterface
         $requestContext = new RequestContext(
             '',
             $request->getMethod(),
-            (string)idn_to_ascii($uri->getHost()),
+            $uri->getHost() ? (string)idn_to_ascii($uri->getHost()) : '',
             $uri->getScheme(),
             // Ports are only necessary for URL generation in Symfony which is not used by TYPO3
             80,