diff --git a/cmd/ulid/main.go b/cmd/ulid/main.go
index ee4173b..50e62cc 100644
--- a/cmd/ulid/main.go
+++ b/cmd/ulid/main.go
@@ -14,7 +14,7 @@ import (
 
 const (
 	defaultms = "Mon Jan 02 15:04:05.999 MST 2006"
-	rfc3339ms = "2006-01-02T15:04:05.999MST"
+	rfc3339ms = "2006-01-02T15:04:05.000Z07:00"
 )
 
 func main() {