diff --git a/src/DocumentXmlReader.php b/src/DocumentXmlReader.php
index bd1f83f..5798c6a 100644
--- a/src/DocumentXmlReader.php
+++ b/src/DocumentXmlReader.php
@@ -228,7 +228,7 @@ private function isXRechnungCII(\DOMDocument $document): bool
             return false;
         }
 
-        return str_contains($result, 'kosit:xrechnung_3.0');
+        return str_contains($result, 'kosit:standard:xrechnung_2.1');
     }
 
     private function isPeppol(\DOMDocument $document): bool