diff --git a/_config.php b/_config.php
index 87cc8bb..d2674ca 100644
--- a/_config.php
+++ b/_config.php
@@ -9,7 +9,7 @@
 \SilverStripe\View\Parsers\ShortcodeParser::get('default')->unregister('embed');
 \SilverStripe\View\Parsers\ShortcodeParser::get('default')->register(
     'embed',
-    function ($arguments, $content = null, $parser = null, $tagName) {
+    function ($arguments, $content = null, $parser = null, $tagName = null) {
         return \Dynamic\CoreTools\View\CTEmbedShortcodeProvider::handle_shortcode(
             $arguments,
             $content,