diff --git a/src/wp-admin/includes/misc.php b/src/wp-admin/includes/misc.php
index 02aa8a8794..94cb43848d 100644
--- a/src/wp-admin/includes/misc.php
+++ b/src/wp-admin/includes/misc.php
@@ -196,6 +196,8 @@ function insert_with_markers( $filename, $marker, $insertion ) {
  * @since 1.5.0
  *
  * @global WP_Rewrite $wp_rewrite
+ *
+ * @return bool|null True on write success, false on failure. Null in multisite.
  */
 function save_mod_rewrite_rules() {
 	if ( is_multisite() ) {
@@ -232,7 +234,7 @@ function save_mod_rewrite_rules() {
  *
  * @global WP_Rewrite $wp_rewrite
  *
- * @return bool True if web.config was updated successfully
+ * @return bool|null True on write success, false on failure. Null in multisite.
  */
 function iis7_save_url_rewrite_rules() {
 	if ( is_multisite() ) {