diff --git a/src/InPageNavigation.php b/src/InPageNavigation.php
index d2ba1bb..92fe879 100644
--- a/src/InPageNavigation.php
+++ b/src/InPageNavigation.php
@@ -11,9 +11,10 @@ private function parseHeading(string $html): object
 	{
 		$matches = [];
 		preg_match('/(id=")(.*?)"/', $html, $matches);
+		$tmp_id = (isset($matches[2])) ? $matches[2] : '';
 		return (object) [
 			'title' => trim(strip_tags($html)),
-			'id' => $matches[2]
+			'id' => $tmp_id
 		];
 	}