diff --git a/contracts/nns/contract.go b/contracts/nns/contract.go
index 7be0b46a..d2a8ef79 100644
--- a/contracts/nns/contract.go
+++ b/contracts/nns/contract.go
@@ -463,12 +463,15 @@ func saveDomain(ctx storage.Context, name, email string, refresh, retry, expire,
 	putSoaRecord(ctx, name, email, refresh, retry, expire, ttl)
 }
 
-// RenewDefault increases domain expiration date for 1 year.
+// RenewDefault increases domain expiration date for 1 year and returns
+// the new expriration timestamp.
 func RenewDefault(name string) int64 {
 	return Renew(name, 1)
 }
 
-// Renew increases domain expiration date up to the specified amount of years.
+// Renew increases domain expiration date up to the specified amount of years
+// (from 1 to 10, can't renew for more than 10 years). Returns new expiration
+// timestamp.
 func Renew(name string, years int) int64 {
 	if years < 1 || years > 10 {
 		panic("invalid renewal period value")