diff --git a/lib/formats/putty.js b/lib/formats/putty.js
index 9d17c0f..89ed0b6 100644
--- a/lib/formats/putty.js
+++ b/lib/formats/putty.js
@@ -64,7 +64,7 @@ function read(buf, options) {
 		assert.equal(parts[0].toLowerCase(), 'private-lines');
 		var privateLines = parseInt(parts[1], 10);
 		if (!isFinite(privateLines) || privateLines < 0 ||
-			privateLines > lines.length) {
+		    privateLines > lines.length) {
 			throw (new Error('Invalid private-lines count'));
 		}
 
@@ -77,9 +77,7 @@ function read(buf, options) {
 					options.filename, 'PEM'));
 			}
 
-			var iv = Buffer.from(Array
-				.from({length: 16})
-				.map(function () { return 0; }));
+			var iv = Buffer.alloc(16, 0);
 			var decipher = crypto.createDecipheriv(
 				'aes-256-cbc',
 				derivePPK2EncryptionKey(options.passphrase),
@@ -95,20 +93,35 @@ function read(buf, options) {
 		}
 
 		var sshbuf = new SSHBuffer({buffer: privateBuf});
+		var privateKeyParts;
 		if (alg === 'ssh-dss') {
-			key.addPart('x', sshbuf.readPart());
+			privateKeyParts = [ {
+				name: 'x',
+				data: sshbuf.readBuffer()
+			}];
 		} else if (alg === 'ssh-rsa') {
-			key.addPart('d', sshbuf.readPart());
-			key.addPart('p', sshbuf.readPart());
-			key.addPart('q', sshbuf.readPart());
-			key.addPart('iqmp', sshbuf.readPart());
+			privateKeyParts = [
+				{ name: 'd', data: sshbuf.readBuffer() },
+				{ name: 'p', data: sshbuf.readBuffer() },
+				{ name: 'q', data: sshbuf.readBuffer() },
+				{ name: 'iqmp', data: sshbuf.readBuffer() }
+			];
 		} else if (alg.startsWith('ecdsa-sha2-nistp')) {
-			key.addPart('d', sshbuf.readPart());
+			privateKeyParts = [ {
+				name: 'd', data: sshbuf.readBuffer()
+			} ];
 		} else if (alg === 'ssh-ed25519') {
-			key.addPart('k', sshbuf.readPart());
+			privateKeyParts = [ {
+				name: 'k', data: sshbuf.readBuffer()
+			} ];
 		} else {
 			throw new Error('Unsupported PPK key type: ' + alg);
 		}
+
+		key = new PrivateKey({
+			type: key.type,
+			parts: key.parts.concat(privateKeyParts)
+		});
 	}
 
 	key.comment = comment;
diff --git a/lib/key.js b/lib/key.js
index e6e892f..706f834 100644
--- a/lib/key.js
+++ b/lib/key.js
@@ -80,12 +80,6 @@ function Key(opts) {
 
 Key.formats = formats;
 
-Key.prototype.addPart = function (name, options) {
-	var part = Object.assign({ name: name }, options);
-	this.parts.push(part);
-	this.part[part.name] = part;
-};
-
 Key.prototype.toBuffer = function (format, options) {
 	if (format === undefined)
 		format = 'ssh';