diff --git a/core/modules/forum/src/ForumManagerInterface.php b/core/modules/forum/src/ForumManagerInterface.php
index 097d36a..89d836f 100644
--- a/core/modules/forum/src/ForumManagerInterface.php
+++ b/core/modules/forum/src/ForumManagerInterface.php
@@ -64,6 +64,9 @@ public function resetCache();
    *
    * @return array
    *   Array of parent terms.
+   *
+   * @deprecated Scheduled to be removed in 9.0.x, see
+   *   https://www.drupal.org/node/2371593.
    */
   public function getParents($tid);