diff --git c/core/modules/comment/comment.module w/core/modules/comment/comment.module
index 32adfec..3597db0 100644
--- c/core/modules/comment/comment.module
+++ w/core/modules/comment/comment.module
@@ -1314,7 +1314,7 @@ function comment_load($cid, $reset = FALSE) {
  *   The number of new comments or FALSE if the user is not logged in.
  */
 function comment_num_new($nid, $timestamp = 0) {
-  global $user;
+  $user = Drupal::currentUser();
 
   if ($user->isAuthenticated() && Drupal::moduleHandler()->moduleExists('history')) {
     // Retrieve the timestamp at which the current user last viewed this node.
@@ -1406,7 +1406,7 @@ function comment_get_display_page($cid, $node_type) {
  * @param Drupal\comment\Comment $comment
  */
 function comment_preview(Comment $comment) {
-  global $user;
+  $user = Drupal::currentUser();
   $preview_build = array();
 
   if (!form_get_errors()) {
@@ -1622,7 +1622,7 @@ function template_preprocess_comment(&$variables) {
  */
 function theme_comment_post_forbidden($variables) {
   $node = $variables['node'];
-  global $user;
+  $user = Drupal::currentUser();
 
   // Since this is expensive to compute, we cache it so that a page with many
   // comments only has to query the database once for all the links.