diff --git a/Validity.md b/Validity.md
index b0657347..6814ffdd 100644
--- a/Validity.md
+++ b/Validity.md
@@ -19,7 +19,7 @@ acme.sh --issue  -d  example.com  -dns dns_cf    --valid-to  "2022-04-01T08:10:3
 
 The value of `--valid-to` is an absolute date time in the future.   The issued cert will expire on that time(`NotAfter`).
 
-Please be careful about the date time format,  it Must be exact format used above.
+Please be careful about the date time format,  it Must be the exact format in UTC used above.