diff --git a/core/types/transaction_signing.go b/core/types/transaction_signing.go
index 95b02f7654..9b782147c5 100644
--- a/core/types/transaction_signing.go
+++ b/core/types/transaction_signing.go
@@ -181,6 +181,7 @@ type Signer interface {
 }
 
 // modernSigner is the signer implementation that handles non-legacy transaction types.
+// For legacy transactions, it defers to one of the legacy signers (frontier, homestead, eip155).
 type modernSigner struct {
 	txtypes map[byte]struct{}
 	chainID *big.Int