diff -u b/core/includes/theme.inc b/core/includes/theme.inc
--- b/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -978,7 +978,7 @@
 
     $variables['links'] = array();
     foreach ($links as $key => $link) {
-      $item = array('link_key' => $key);
+      $item = array();
       $link += array(
         'ajax' => NULL,
         'url' => NULL,
@@ -1040,7 +1040,7 @@
       $item['attributes'] = new Attribute($li_attributes);
 
       // Add the item to the list of links.
-      $variables['links'][] = $item;
+      $variables['links'][$key] = $item;
     }
   }
 }
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
@@ -45,8 +45,8 @@
     {%- endif -%}
   {%- endif -%}
   <ul{{ attributes }}>
-    {%- for item in links -%}
-      <li{{ item.attributes.addClass(item.link_key|clean_class) }}>
+    {%- for key, item in links -%}
+      <li{{ item.attributes.addClass(key|clean_class) }}>
         {%- if item.link -%}
           {{ item.link }}
         {%- elseif item.text_attributes -%}