diff --git a/tests/src/Cas/Protocol/Cas20Test.php b/tests/src/Cas/Protocol/Cas20Test.php
index 79c670e4..1517ef3b 100644
--- a/tests/src/Cas/Protocol/Cas20Test.php
+++ b/tests/src/Cas/Protocol/Cas20Test.php
@@ -54,6 +54,6 @@ public function testAttributeToXmlConversion(): void
 
         $xml = $casProtocol->getValidateSuccessResponse('myUser');
 
-        $this->assertEquals($this->document->saveXML(), $xml);
+        $this->assertEquals($this->document->saveXML(), strval($xml));
     }
 }