diff --git a/src/DOMNodeComparator.php b/src/DOMNodeComparator.php
index 38f30f1..ae5da1d 100644
--- a/src/DOMNodeComparator.php
+++ b/src/DOMNodeComparator.php
@@ -71,7 +71,10 @@ private function nodeToText(DOMNode $node, bool $canonicalize, bool $ignoreCase)
     {
         if ($canonicalize) {
             $document = new DOMDocument;
-            @$document->loadXML('<?xml version="1.0" encoding="' . $node->ownerDocument->encoding . '"?>' . \PHP_EOL . $node->C14N());
+            @$document->loadXML(
+                '<?xml version="1.0" encoding="' . ($node->ownerDocument->encoding ?: 'UTF-8') . '"?>' . \PHP_EOL
+                . $node->C14N()
+            );
 
             $node = $document;
         }