diff --git a/src/XPath/XPath.php b/src/XPath/XPath.php
index d1b4575f..0f22ad55 100644
--- a/src/XPath/XPath.php
+++ b/src/XPath/XPath.php
@@ -124,13 +124,11 @@ private static function registerAncestorNamespaces(DOMXPath $xp, DOMNode $node):
                     if ($attr->namespaceURI !== C_XML::NS_XMLNS) {
                         continue;
                     }
-                    $prefix = $attr->localName;
+                    $prefix = $attr->prefix;
                     $uri = (string) $attr->nodeValue;
 
                     if (
-                        $prefix === null || $prefix === '' ||
-                        $prefix === 'xmlns' || $uri === '' ||
-                        isset($prefixToUri[$prefix])
+                        $prefix === '' || $prefix === 'xmlns' || $uri === '' || isset($prefixToUri[$prefix])
                     ) {
                         continue;
                     }