diff --git a/core/lib/Drupal/Component/Utility/Xss.php b/core/lib/Drupal/Component/Utility/Xss.php
index 4c6e812694e..f967ca6264c 100644
--- a/core/lib/Drupal/Component/Utility/Xss.php
+++ b/core/lib/Drupal/Component/Utility/Xss.php
@@ -143,11 +143,10 @@ class Xss {
       return '<';
     }
 
-    if (!preg_match('%^<\s*(/\s*)?([a-zA-Z0-9\-]+)([^>]*)>?|(<!--.*?-->)$%', $string, $matches)) {
+    if (!preg_match('%^<\s*(/\s*)?([a-zA-Z0-9\-]+)\s*([^>]*)>?|(<!--.*?-->)$%', $string, $matches)) {
       // Seriously malformed.
       return '';
     }
-
     $slash = trim($matches[1]);
     $elem = &$matches[2];
     $attrlist = &$matches[3];