diff -u b/lib/Drupal/pgn/Tests/XmlEncoderUnitTest.php b/lib/Drupal/pgn/Tests/XmlEncoderUnitTest.php
--- b/lib/Drupal/pgn/Tests/XmlEncoderUnitTest.php
+++ b/lib/Drupal/pgn/Tests/XmlEncoderUnitTest.php
@@ -8857,11 +8857,12 @@
       ),
     ),
   ),
+  '@xmlns' => 'x-schema:pgn.xdr',
 );
 
   protected $pgnxml = <<<'EOPGNXML'
 <?xml version="1.0"?>
-<PGNGAMES>
+<PGNGAMES xmlns="x-schema:pgn.xdr">
 <game>
 <info>
 <Event>Salzburg</Event>