diff --git a/ext/dom/parentnode/tree.c b/ext/dom/parentnode/tree.c
index 51cdd7cff43..9fb682910f0 100644
--- a/ext/dom/parentnode/tree.c
+++ b/ext/dom/parentnode/tree.c
@@ -500,7 +500,7 @@ static void dom_insert_node_list_cleanup(xmlNodePtr node)
 		xmlFreeNode(node);
 	} else {
 		/* Must have been a directly-passed node. */
-		ZEND_ASSERT(node->_private != NULL);
+		ZEND_UNREACHABLE();
 	}
 }