diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 2786774..cd2f449 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1022,7 +1022,7 @@ function template_preprocess_links(&$variables) {
 
     $variables['links'] = array();
     foreach ($links as $key => $link) {
-      $item = array();
+      $item = array('key' => $key);
       $link += array(
         'href' => NULL,
         'route_name' => NULL,
@@ -1030,10 +1030,6 @@ function template_preprocess_links(&$variables) {
         'ajax' => NULL,
       );
 
-      $li_attributes = array('class' => array());
-      // Use the array key as class name.
-      $li_attributes['class'][] = drupal_html_class($key);
-
       $keys = array('title', 'href', 'route_name', 'route_parameters');
       $link_element = array(
         '#type' => 'link',
@@ -1047,6 +1043,7 @@ function template_preprocess_links(&$variables) {
 
       // Handle links and ensure that the active class is added on the LIs, but
       // only if the 'set_active_class' option is not empty.
+      $li_attributes = array();
       if (isset($link['href']) || isset($link['route_name'])) {
         if (!empty($variables['set_active_class'])) {
 
diff --git a/core/modules/system/src/Tests/Theme/FunctionsTest.php b/core/modules/system/src/Tests/Theme/FunctionsTest.php
index 58ffcde..9eaa263 100644
--- a/core/modules/system/src/Tests/Theme/FunctionsTest.php
+++ b/core/modules/system/src/Tests/Theme/FunctionsTest.php
@@ -269,13 +269,13 @@ function testLinks() {
     $variables['set_active_class'] = TRUE;
     $expected_links = '';
     $expected_links .= '<ul id="somelinks">';
-    $expected_links .= '<li class="a-link" data-drupal-link-system-path="a/link"><a href="' . url('a/link') . '" class="a/class" data-drupal-link-system-path="a/link">' . String::checkPlain('A <link>') . '</a></li>';
+    $expected_links .= '<li data-drupal-link-system-path="a/link" class="a-link"><a href="' . url('a/link') . '" class="a/class" data-drupal-link-system-path="a/link">' . String::checkPlain('A <link>') . '</a></li>';
     $expected_links .= '<li class="plain-text"><span class="a/class">' . String::checkPlain('Plain "text"') . '</span></li>';
-    $expected_links .= '<li class="front-page" data-drupal-link-system-path="&lt;front&gt;"><a href="' . url('<front>') . '" data-drupal-link-system-path="&lt;front&gt;">' . String::checkPlain('Front page') . '</a></li>';
-    $expected_links .= '<li class="router-test" data-drupal-link-system-path="router_test/test1"><a href="' . \Drupal::urlGenerator()->generate('router_test.1') . '" data-drupal-link-system-path="router_test/test1">' . String::checkPlain('Test route') . '</a></li>';
+    $expected_links .= '<li data-drupal-link-system-path="&lt;front&gt;" class="front-page"><a href="' . url('<front>') . '" data-drupal-link-system-path="&lt;front&gt;">' . String::checkPlain('Front page') . '</a></li>';
+    $expected_links .= '<li data-drupal-link-system-path="router_test/test1" class="router-test"><a href="' . \Drupal::urlGenerator()->generate('router_test.1') . '" data-drupal-link-system-path="router_test/test1">' . String::checkPlain('Test route') . '</a></li>';
     $query = array('key' => 'value');
     $encoded_query = String::checkPlain(Json::encode($query));
-    $expected_links .= '<li class="query-test" data-drupal-link-query="'.$encoded_query.'" data-drupal-link-system-path="router_test/test1"><a href="' . \Drupal::urlGenerator()->generate('router_test.1', $query) . '" data-drupal-link-query="'.$encoded_query.'" data-drupal-link-system-path="router_test/test1">' . String::checkPlain('Query test route') . '</a></li>';
+    $expected_links .= '<li data-drupal-link-query="'.$encoded_query.'" data-drupal-link-system-path="router_test/test1" class="query-test"><a href="' . \Drupal::urlGenerator()->generate('router_test.1', $query) . '" data-drupal-link-query="'.$encoded_query.'" data-drupal-link-system-path="router_test/test1">' . String::checkPlain('Query test route') . '</a></li>';
     $expected_links .= '</ul>';
     $expected = $expected_heading . $expected_links;
     $this->assertThemeOutput('links', $variables, $expected);
diff --git a/core/modules/system/templates/links.html.twig b/core/modules/system/templates/links.html.twig
index 3823c22..06cb8f1 100644
--- a/core/modules/system/templates/links.html.twig
+++ b/core/modules/system/templates/links.html.twig
@@ -15,6 +15,7 @@
  *     not be passed through \Drupal\Component\Utility\String::checkPlain().
  *   - attributes: (optional) HTML attributes for the anchor, or for the <span>
  *     tag if no 'href' is supplied.
+ *   - key: The link key. To be used as link class.
  * - heading: (optional) A heading to precede the links.
  *   - text: The heading text.
  *   - level: The heading level (e.g. 'h2', 'h3').
@@ -45,7 +46,7 @@
   {%- endif -%}
   <ul{{ attributes }}>
     {%- for item in links -%}
-      <li{{ item.attributes }}>
+      <li{{ item.attributes.addClass(item.key|clean_class) }}>
         {%- if item.link -%}
           {{ item.link }}
         {%- elseif item.text_attributes -%}