diff --git a/lib/demo.php b/lib/demo.php
index 11272050bf4c2e..0e7ad5c2c8cc78 100644
--- a/lib/demo.php
+++ b/lib/demo.php
@@ -11,6 +11,8 @@
 
 /**
  * Redirects the demo page to edit a new post.
+ *
+ * @global string $pagenow The name of the current admin page being viewed.
  */
 function gutenberg_redirect_demo() {
 	global $pagenow;