diff --git a/core/types/transaction.go b/core/types/transaction.go
index ba3d5de91..3eb8df0ac 100644
--- a/core/types/transaction.go
+++ b/core/types/transaction.go
@@ -252,7 +252,9 @@ func (tx *Transaction) Cost() *big.Int {
 	return total
 }
 
-func (tx *Transaction) RawSignatureValues() (*big.Int, *big.Int, *big.Int) {
+// RawSignatureValues returns the V, R, S signature values of the transaction.
+// The return values should not be modified by the caller.
+func (tx *Transaction) RawSignatureValues() (v, r, s *big.Int) {
 	return tx.data.V, tx.data.R, tx.data.S
 }