diff --git a/core/modules/system/templates/menu.html.twig b/core/modules/system/templates/menu.html.twig
index 0722334..3151454 100644
--- a/core/modules/system/templates/menu.html.twig
+++ b/core/modules/system/templates/menu.html.twig
@@ -26,7 +26,11 @@
 {% macro menu_links(items, menu_level) %}
   {% import _self as menus %}
   {% if items %}
-    <ul class="menu">
+    {% if menu_level is 0 %}
+      <ul {{ attributes.addClass('menu') }}>
+    {% else %}
+      <ul class="menu">
+    {%  endif %}
       {% for item in items %}
         <li{{ item.attributes }}>
           {{ link_from_url(item.title, item.url) }}