diff --git a/src/HTMLConverter.php b/src/HTMLConverter.php
index e3458249..8a7c6bdd 100644
--- a/src/HTMLConverter.php
+++ b/src/HTMLConverter.php
@@ -96,11 +96,13 @@ protected function appendHeaderSection(string $node_name, array $record, DOMElem
             return;
         }
 
+        /** @var DOMDocument $ownerDocument */
+        $ownerDocument = $table->ownerDocument;
         $node = $this->xml_converter
             ->rootElement($node_name)
             ->recordElement('tr')
             ->fieldElement('th')
-            ->import([$record], $table->ownerDocument)
+            ->import([$record], $ownerDocument)
         ;
 
         /** @var DOMElement $element */