diff --git a/lib/certificate.js b/lib/certificate.js
index 49514b5..4fbe6ab 100644
--- a/lib/certificate.js
+++ b/lib/certificate.js
@@ -128,10 +128,19 @@ Certificate.prototype.isSignedByKey = function (issuerKey) {
 };
 
 Certificate.prototype.signWith = function (key) {
+	utils.assertCompatible(key, PrivateKey, [1, 2], 'key');
 	var fmts = Object.keys(formats);
+	var didOne = false;
 	for (var i = 0; i < fmts.length; ++i) {
-		if (fmts[i] !== 'pem')
-			formats[fmts[i]].sign(this, key);
+		if (fmts[i] !== 'pem') {
+			var ret = formats[fmts[i]].sign(this, key);
+			if (ret === true)
+				didOne = true;
+		}
+	}
+	if (!didOne) {
+		throw (new Error('Failed to sign the certificate for any ' +
+		    'available certificate formats'));
 	}
 };
 
diff --git a/lib/formats/openssh-cert.js b/lib/formats/openssh-cert.js
index a8cfb75..8ce7350 100644
--- a/lib/formats/openssh-cert.js
+++ b/lib/formats/openssh-cert.js
@@ -58,6 +58,8 @@ function fromBuffer(data, algo, partial) {
 	var innerAlgo = sshbuf.readString();
 	if (algo !== undefined && innerAlgo !== algo)
 		throw (new Error('SSH certificate algorithm mismatch'));
+	if (algo === undefined)
+		algo = innerAlgo;
 
 	var cert = {};
 	cert.signatures = {};
@@ -168,15 +170,22 @@ function dateToInt64(date) {
 }
 
 function sign(cert, key) {
-	assert.ok(PrivateKey.isPrivateKey(key, [1, 2]));
 	if (cert.signatures.openssh === undefined)
 		cert.signatures.openssh = {};
+	try {
+		var blob = toBuffer(cert, true);
+	} catch (e) {
+		delete (cert.signatures.openssh);
+		return (false);
+	}
 	var sig = cert.signatures.openssh;
-
-	var blob = toBuffer(cert, true);
-	var signer = key.createSign();
+	var hashAlgo = undefined;
+	if (key.type === 'rsa' || key.type === 'dsa')
+		hashAlgo = 'sha1';
+	var signer = key.createSign(hashAlgo);
 	signer.write(blob);
 	sig.signature = signer.sign();
+	return (true);
 }
 
 function write(cert, options) {
@@ -262,6 +271,8 @@ function getAlg(certType) {
 		return ('dsa');
 	if (certType.match(ECDSA_ALGO))
 		return ('ecdsa');
+	if (certType === 'ssh-ed25519-cert-v01@openssh.com')
+		return ('ed25519');
 	throw (new Error('Unsupported cert type ' + certType));
 }
 
@@ -272,5 +283,7 @@ function getCertType(key) {
 		return ('ssh-dss-cert-v01@openssh.com');
 	if (key.type === 'ecdsa')
 		return ('ecdsa-sha2-' + key.curve + '-cert-v01@openssh.com');
+	if (key.type === 'ed25519')
+		return ('ssh-ed25519-cert-v01@openssh.com');
 	throw (new Error('Unsupported key type ' + key.type));
 }
diff --git a/lib/formats/x509.js b/lib/formats/x509.js
index 6e9b1f5..34f70b8 100644
--- a/lib/formats/x509.js
+++ b/lib/formats/x509.js
@@ -338,7 +338,8 @@ function sign(cert, key) {
 	var sig = cert.signatures.x509;
 
 	sig.algo = key.type + '-' + key.defaultHashAlgorithm();
-	assert.string(SIGN_ALGS[sig.algo]);
+	if (SIGN_ALGS[sig.algo] === undefined)
+		return (false);
 
 	var der = new asn1.BerWriter();
 	writeTBSCert(cert, der);
@@ -348,6 +349,8 @@ function sign(cert, key) {
 	var signer = key.createSign();
 	signer.write(blob);
 	cert.signatures.x509.signature = signer.sign();
+
+	return (true);
 }
 
 function write(cert, options) {
diff --git a/package.json b/package.json
index eebac23..98f3d6e 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "sshpk",
-  "version": "1.9.0",
+  "version": "1.9.1",
   "description": "A library for finding and using SSH public keys",
   "main": "lib/index.js",
   "scripts": {
diff --git a/test/certs.js b/test/certs.js
index 16bca48..e3e479f 100644
--- a/test/certs.js
+++ b/test/certs.js
@@ -14,6 +14,7 @@ var GEORGE_KEY, GEORGE_SSH, GEORGE_X509;
 var BARRY_KEY;
 var JIM_KEY, JIM_SSH, JIM_X509;
 var EC_KEY, EC_KEY2;
+var SUE_KEY;
 
 test('setup', function (t) {
 	var d = fs.readFileSync(path.join(testDir, 'id_dsa'));
@@ -34,6 +35,10 @@ test('setup', function (t) {
 	EC_KEY = sshpk.parsePrivateKey(d);
 	d = fs.readFileSync(path.join(testDir, 'id_ecdsa2'));
 	EC2_KEY = sshpk.parsePrivateKey(d);
+
+	d = fs.readFileSync(path.join(testDir, 'id_ed25519'));
+	SUE_KEY = sshpk.parsePrivateKey(d);
+
 	t.end();
 });
 
@@ -169,6 +174,26 @@ test('create ecdsa signed, loopback', function (t) {
 	t.end();
 });
 
+test('create ed25519 self-signed, loopback', function (t) {
+	var id = sshpk.identityForHost('foobar.com');
+	var cert = sshpk.createSelfSignedCertificate(id, SUE_KEY);
+
+	t.throws(function () {
+		cert.toBuffer('pem');
+	});
+	t.throws(function () {
+		cert.toBuffer('x509');
+	});
+
+	var ossh = cert.toBuffer('openssh');
+	var cert3 = sshpk.parseCertificate(ossh, 'openssh');
+	t.ok(SUE_KEY.fingerprint().matches(cert3.subjectKey));
+	t.ok(cert3.subjects[0].equals(cert.subjects[0]));
+	t.strictEqual(cert3.subjects[0].hostname, 'foobar.com');
+
+	t.end();
+});
+
 test('subjectaltname', function (t) {
 	var ids = [
 		sshpk.identityForHost('foobar.com'),