diff --git a/40.md b/40.md
index 153309a5..5f67732e 100644
--- a/40.md
+++ b/40.md
@@ -14,7 +14,7 @@ So be careful when sharing confidential information.
 ```
 tag: expiration
 options:
- - [timestamp UTC-0]: required
+ - [UNIX timestamp in seconds]: required
 ```
 
 #### Example