diff --git a/lib/bcoin/ec.js b/lib/bcoin/ec.js
index 5e7c4e92..00d7613f 100644
--- a/lib/bcoin/ec.js
+++ b/lib/bcoin/ec.js
@@ -134,6 +134,52 @@ ec.publicKeyConvert = function publicKeyConvert(key, compressed) {
   return new Buffer(point.encode('array', compressed));
 };
 
+/**
+ * ((tweak + key) % n)
+ * @param {Buffer} privateKey
+ * @param {Buffer} tweak
+ * @returns {Buffer} privateKey
+ */
+
+ec.privateKeyTweakAdd = function privateKeyTweakAdd(privateKey, tweak) {
+  if (secp256k1)
+    return secp256k1.privateKeyTweakAdd(privateKey, tweak);
+
+  privateKey = new bn(tweak)
+    .add(new bn(privateKey))
+    .mod(ec.curve.n)
+    .toArrayLike(Buffer, 'be', 32);
+
+  // Only a 1 in 2^127 chance of happening.
+  if (!ec.privateKeyVerify(privateKey))
+    throw new Error('Private key is invalid.');
+
+  return privateKey;
+};
+
+/**
+ * ((g * tweak) + key)
+ * @param {Buffer} publicKey
+ * @param {Buffer} tweak
+ * @returns {Buffer} publicKey
+ */
+
+ec.publicKeyTweakAdd = function publicKeyTweakAdd(publicKey, tweak, compressed) {
+  var point;
+
+  if (secp256k1)
+    return secp256k1.publicKeyTweakAdd(publicKey, tweak, compressed);
+
+  point = ec.decodePoint(publicKey);
+  point = ec.curve.g.mul(new bn(tweak)).add(point);
+  publicKey = new Buffer(point.encode('array', compressed));
+
+  if (!ec.publicKeyVerify(publicKey))
+    throw new Error('Public key is invalid.');
+
+  return publicKey;
+};
+
 /**
  * Create an ecdh.
  * @param {Buffer} pub
diff --git a/lib/bcoin/hd.js b/lib/bcoin/hd.js
index ac039274..3cd0dd7f 100644
--- a/lib/bcoin/hd.js
+++ b/lib/bcoin/hd.js
@@ -945,7 +945,7 @@ HDPrivateKey.prototype.__defineGetter__('xpubkey', function() {
  */
 
 HDPrivateKey.prototype.derive = function derive(index, hardened) {
-  var p, id, data, hash, left, chainCode, privateKey, child;
+  var p, id, data, hash, left, right, privateKey, child;
 
   if (typeof index === 'string')
     return this.derivePath(index);
@@ -981,17 +981,14 @@ HDPrivateKey.prototype.derive = function derive(index, hardened) {
   data = p.render();
 
   hash = utils.hmac('sha512', data, this.chainCode);
-  left = new bn(hash.slice(0, 32));
-  chainCode = hash.slice(32, 64);
+  left = hash.slice(0, 32);
+  right = hash.slice(32, 64);
 
-  privateKey = left
-    .add(new bn(this.privateKey))
-    .mod(ec.curve.n)
-    .toArrayLike(Buffer, 'be', 32);
-
-  // Only a 1 in 2^127 chance of happening.
-  if (!ec.privateKeyVerify(privateKey))
-    throw new Error('Private key is invalid.');
+  try {
+    privateKey = ec.privateKeyTweakAdd(this.privateKey, left);
+  } catch (e) {
+    return this.derive(index + 1);
+  }
 
   if (!this.fingerPrint)
     this.fingerPrint = utils.hash160(this.publicKey).slice(0, 4);
@@ -1001,7 +998,7 @@ HDPrivateKey.prototype.derive = function derive(index, hardened) {
   child.depth = this.depth + 1;
   child.parentFingerPrint = this.fingerPrint;
   child.childIndex = index;
-  child.chainCode = chainCode;
+  child.chainCode = right;
   child.privateKey = privateKey;
   child.publicKey = ec.publicKeyCreate(privateKey, true);
 
@@ -1179,7 +1176,7 @@ HDPrivateKey.prototype.equal = function equal(obj) {
  */
 
 HDPrivateKey.prototype.fromSeed = function fromSeed(seed, network) {
-  var hash, chainCode, privateKey;
+  var hash, left, right;
 
   assert(Buffer.isBuffer(seed));
 
@@ -1190,19 +1187,19 @@ HDPrivateKey.prototype.fromSeed = function fromSeed(seed, network) {
 
   hash = utils.hmac('sha512', seed, 'Bitcoin seed');
 
-  privateKey = hash.slice(0, 32);
-  chainCode = hash.slice(32, 64);
+  left = hash.slice(0, 32);
+  right = hash.slice(32, 64);
 
   // Only a 1 in 2^127 chance of happening.
-  if (!ec.privateKeyVerify(privateKey))
+  if (!ec.privateKeyVerify(left))
     throw new Error('Master private key is invalid.');
 
   this.network = bcoin.network.get(network);
   this.depth = 0;
   this.parentFingerPrint = new Buffer([0, 0, 0, 0]);
   this.childIndex = 0;
-  this.chainCode = chainCode;
-  this.privateKey = privateKey;
+  this.chainCode = right;
+  this.privateKey = left;
   this.publicKey = ec.publicKeyCreate(this.privateKey, true);
 
   return this;
@@ -1597,7 +1594,7 @@ HDPublicKey.prototype.__defineGetter__('xpubkey', function() {
  */
 
 HDPublicKey.prototype.derive = function derive(index, hardened) {
-  var p, id, data, hash, left, chainCode, point, publicKey, child;
+  var p, id, data, hash, left, right, publicKey, child;
 
   if (typeof index === 'string')
     return this.derivePath(index);
@@ -1623,16 +1620,14 @@ HDPublicKey.prototype.derive = function derive(index, hardened) {
   data = p.render();
 
   hash = utils.hmac('sha512', data, this.chainCode);
-  left = new bn(hash.slice(0, 32));
-  chainCode = hash.slice(32, 64);
+  left = hash.slice(0, 32);
+  right = hash.slice(32, 64);
 
-  point = ec.decodePoint(this.publicKey);
-  point = ec.curve.g.mul(left).add(point);
-  publicKey = new Buffer(point.encode('array', true));
-  assert(publicKey.length === 33);
-
-  if (!ec.publicKeyVerify(publicKey))
-    throw new Error('Public key is invalid.');
+  try {
+    publicKey = ec.publicKeyTweakAdd(this.publicKey, left, true);
+  } catch (e) {
+    return this.derive(index + 1);
+  }
 
   if (!this.fingerPrint)
     this.fingerPrint = utils.hash160(this.publicKey).slice(0, 4);
@@ -1642,7 +1637,7 @@ HDPublicKey.prototype.derive = function derive(index, hardened) {
   child.depth = this.depth + 1;
   child.parentFingerPrint = this.fingerPrint;
   child.childIndex = index;
-  child.chainCode = chainCode;
+  child.chainCode = right;
   child.publicKey = publicKey;
 
   HD.cache.set(id, child);