diff --git a/modules/system/system.api.php b/modules/system/system.api.php
index 22ad7a6..51d6eab 100644
--- a/modules/system/system.api.php
+++ b/modules/system/system.api.php
@@ -2761,8 +2761,9 @@ function hook_file_url_alter(&$uri) {
 /**
  * Check installation requirements and do status reporting.
  *
- * This hook has two closely related uses, determined by the $phase argument:
+ * This hook has three closely related uses, determined by the $phase argument:
  * checking installation requirements ($phase == 'install')
+ * checking update requirements ($phase == 'update')
  * and status reporting ($phase == 'runtime').
  *
  * Note that this hook, like all others dealing with installation and updates,