diff --git a/wp-includes/post.php b/wp-includes/post.php
index 669026ecf0..f46bb8c65f 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -1813,7 +1813,7 @@ function delete_post_meta($post_id, $meta_key, $meta_value = '') {
  *
  * @param int $post_id Post ID.
  * @param string $key Optional. The meta key to retrieve. By default, returns data for all keys.
- * @param bool $single Whether to return a single value.
+ * @param bool $single Optional. Whether to return a single value.
  * @return mixed Will be an array if $single is false. Will be value of meta data field if $single
  *  is true.
  */