Index: src/wp-includes/functions.php
===================================================================
--- src/wp-includes/functions.php	(revision 40950)
+++ src/wp-includes/functions.php	(working copy)
@@ -5455,6 +5455,8 @@
  * This prevents reusing the same tab for a preview when the user has navigated away.
  *
  * @since 4.3.0
+ *
+ * @global $post
  */
 function wp_post_preview_js() {
 	global $post;