diff --git a/system/cache/file.php b/system/cache/file.php
index 06616ea1..ec3187d1 100644
--- a/system/cache/file.php
+++ b/system/cache/file.php
@@ -29,6 +29,8 @@ public function get($key)
 
 		$cache = file_get_contents(CACHE_PATH.$key);
 
+		// The cache expiration date is stored as a UNIX timestamp at the beginning
+		// of the cache file. We'll extract it out and check it here.
 		if (time() >= substr($cache, 0, 10))
 		{
 			$this->forget($key);