diff -u b/core/modules/system/templates/table.html.twig b/core/modules/system/templates/table.html.twig
--- b/core/modules/system/templates/table.html.twig
+++ b/core/modules/system/templates/table.html.twig
@@ -49,7 +49,7 @@
         {% endfor %}
       </colgroup>
     {% else %}
-      <colgroup{{ colgroup.attributes }} />
+      <colgroup{{ colgroup.attributes }}></colgroup>
     {% endif %}
   {% endfor %}