diff -u b/core/includes/theme.inc b/core/includes/theme.inc
--- b/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1685,14 +1685,4 @@
   $heading = &$variables['heading'];
 
-  // Remove 'links' from the attributes array. This is added through
-  // template_preprocess() but we do not need it.
-  if (isset($variables['attributes']['class'][0]) && $variables['attributes']['class'][0] == 'links') {
-    unset($variables['attributes']['class'][0]);
-    if (empty($variables['attributes']['class'])) {
-      unset($variables['attributes']['class']);
-    }
-  }
-  $variables['attributes'] = new Attribute($variables['attributes']);
-
   if (!empty($links)) {
     // Prepend the heading to the list, if any.
diff -u b/core/modules/system/templates/links.html.twig b/core/modules/system/templates/links.html.twig
--- b/core/modules/system/templates/links.html.twig
+++ b/core/modules/system/templates/links.html.twig
@@ -17,10 +17,9 @@
  *     tag if no 'href' is supplied.
  * - heading: (optional) A heading to precede the links. May be an associative
  *   array or a string.
- *   If the heading is an array, it can have the following elements:
  *   - text: The heading text.
  *   - level: The heading level (e.g. 'h2', 'h3').
- *   - attributes: (optional) A keyed array of attributes for the heading.
+ *   - attributes: (optional) A keyed list of attributes for the heading.
  *   If the heading is a string, it will be used as the text of the heading and
  *   the level will default to 'h2'.
  *