diff --git a/src/crypto/x509/x509.go b/src/crypto/x509/x509.go
index 7bca6810f7d..d959d0ba3fb 100644
--- a/src/crypto/x509/x509.go
+++ b/src/crypto/x509/x509.go
@@ -99,7 +99,7 @@ func marshalPublicKey(pub interface{}) (publicKeyBytes []byte, publicKeyAlgorith
 		publicKeyBytes = pub
 		publicKeyAlgorithm.Algorithm = oidPublicKeyEd25519
 	default:
-		return nil, pkix.AlgorithmIdentifier{}, errors.New("x509: only RSA and ECDSA public keys supported")
+		return nil, pkix.AlgorithmIdentifier{}, fmt.Errorf("x509: unsupported public key type: %T", pub)
 	}
 
 	return publicKeyBytes, publicKeyAlgorithm, nil