diff --git a/src/wp-includes/pluggable.php b/src/wp-includes/pluggable.php
index 99193eaf2e..d394567e4a 100644
--- a/src/wp-includes/pluggable.php
+++ b/src/wp-includes/pluggable.php
@@ -1270,6 +1270,9 @@ function wp_sanitize_redirect($location) {
  * @access private
  *
  * @see wp_sanitize_redirect()
+ *
+ * @param array $matches RegEx matches against the redirect location.
+ * @return string URL-encoded version of the first RegEx match.
  */
 function _wp_sanitize_utf8_in_redirect( $matches ) {
 	return urlencode( $matches[0] );