diff --git a/src/wp-includes/user.php b/src/wp-includes/user.php
index 028606385b..6f5dae67f9 100644
--- a/src/wp-includes/user.php
+++ b/src/wp-includes/user.php
@@ -420,7 +420,7 @@ function count_many_users_posts( $users, $post_type = 'post', $public_only = fal
  *
  * @since MU
  *
- * @return int The current user's ID
+ * @return int The current user's ID, or 0 if no user is logged in.
  */
 function get_current_user_id() {
 	if ( ! function_exists( 'wp_get_current_user' ) )