diff --git a/wp-includes/cache.php b/wp-includes/cache.php
index 933c7b2ec1..af1c2adac9 100644
--- a/wp-includes/cache.php
+++ b/wp-includes/cache.php
@@ -19,7 +19,7 @@
  * @param mixed $data The data to add to the cache store
  * @param string $group The group to add the cache to
  * @param int $expire When the cache data should be expired
- * @return unknown
+ * @return bool False if cache key and group already exist, true on success
  */
 function wp_cache_add($key, $data, $group = '', $expire = 0) {
 	global $wp_object_cache;
@@ -85,7 +85,7 @@ function wp_cache_delete($key, $group = '') {
  * @uses $wp_object_cache Object Cache Class
  * @see WP_Object_Cache::flush()
  *
- * @return bool Always returns true
+ * @return bool False on failure, true on success
  */
 function wp_cache_flush() {
 	global $wp_object_cache;
@@ -152,7 +152,7 @@ function wp_cache_init() {
  * @param mixed $data The contents to store in the cache
  * @param string $group Where to group the cache contents
  * @param int $expire When to expire the cache contents
- * @return bool False if cache key and group already exist, true on success
+ * @return bool False if not exists, true if contents were replaced
  */
 function wp_cache_replace($key, $data, $group = '', $expire = 0) {
 	global $wp_object_cache;
@@ -171,7 +171,7 @@ function wp_cache_replace($key, $data, $group = '', $expire = 0) {
  * @param mixed $data The contents to store in the cache
  * @param string $group Where to group the cache contents
  * @param int $expire When to expire the cache contents
- * @return bool False if cache key and group already exist, true on success
+ * @return bool False on failure, true on success
  */
 function wp_cache_set($key, $data, $group = '', $expire = 0) {
 	global $wp_object_cache;