diff --git a/doc/04-schema.md b/doc/04-schema.md
index bae038fc0..68c50c846 100644
--- a/doc/04-schema.md
+++ b/doc/04-schema.md
@@ -151,7 +151,7 @@ Optional.
 
 Release date of the version.
 
-Must be in `YYYY-MM-DD` or `YYYY-MM-DD HH:MM:SS` format.
+Must be in `YYYY-MM-DD` or `YYYY-MM-DD HH:MM:SS` format in UTC timezone.
 
 Optional.