diff --git a/crypto/crypto.go b/crypto/crypto.go
index f9979aa4bb..13e9b134f0 100644
--- a/crypto/crypto.go
+++ b/crypto/crypto.go
@@ -184,6 +184,9 @@ func UnmarshalPubkey(pub []byte) (*ecdsa.PublicKey, error) {
 	return &ecdsa.PublicKey{Curve: S256(), X: x, Y: y}, nil
 }
 
+// FromECDSAPub converts a secp256k1 public key to bytes.
+// Note: it does not use the curve from pub, instead it always
+// encodes using secp256k1.
 func FromECDSAPub(pub *ecdsa.PublicKey) []byte {
 	if pub == nil || pub.X == nil || pub.Y == nil {
 		return nil