diff --git a/core/modules/node/src/Entity/Node.php b/core/modules/node/src/Entity/Node.php
index afa31e3..413d947 100644
--- a/core/modules/node/src/Entity/Node.php
+++ b/core/modules/node/src/Entity/Node.php
@@ -77,6 +77,9 @@ class Node extends ContentEntityBase implements NodeInterface {
   /**
    * Whether the node is being previewed or not.
    *
+   * The variable is set to public as it will give a considerable performance
+   * improvement. See https://www.drupal.org/node/2498919.
+   *
    * @var true|null
    */
   public $in_preview = NULL;