diff --git a/tests/lib/SimpleSAML/Utils/XMLTest.php b/tests/lib/SimpleSAML/Utils/XMLTest.php
index bac2945866e30bf401cdfe230bab49d2f7e3bd25..dfe64c1648b4402cf0af8310c31c76be0587c961 100644
--- a/tests/lib/SimpleSAML/Utils/XMLTest.php
+++ b/tests/lib/SimpleSAML/Utils/XMLTest.php
@@ -428,7 +428,7 @@ XMLDOC;
         $dom->loadXML($xml, LIBXML_NONET);
 
         $res = XML::isValid($dom, $schema);
-        $this->assertTrue($res);
+        $this->assertTrue($res === true);
     }
 
     /**