diff --git a/lib/bcoin/hd.js b/lib/bcoin/hd.js
index 7dd5aa76..afde473e 100644
--- a/lib/bcoin/hd.js
+++ b/lib/bcoin/hd.js
@@ -104,7 +104,7 @@ var unorm = require('../../vendor/unorm');
  * be generated if not present).
  * @param {String?} options.passphrase - Optional salt for
  * key stretching (empty string if not present).
- * @param {String?} options.lang - Language.
+ * @param {String?} options.language - Language.
  */
 
 function Mnemonic(options) {
@@ -118,7 +118,7 @@ function Mnemonic(options) {
   this.entropy = options.entropy;
   this.phrase = options.phrase;
   this.passphrase = options.passphrase || '';
-  this.lang = options.lang || 'english';
+  this.language = options.language || 'english';
   this.seed = null;
 
   assert(this.bits >= 128);
@@ -154,29 +154,40 @@ Mnemonic.prototype.toSeed = function toSeed() {
  */
 
 Mnemonic.prototype.createMnemonic = function createMnemonic() {
-  var bin = '';
   var mnemonic = [];
-  var wordlist = Mnemonic.getWordlist(this.lang);
-  var i, wi, hash, bits;
+  var bits = this.entropy.length * 8;
+  var wordlist = Mnemonic.getWordlist(this.language);
+  var i, j, word, entropy, oct, bit;
 
-  for (i = 0; i < this.entropy.length; i++)
-    bin += ('00000000' + this.entropy[i].toString(2)).slice(-8);
+  // Append the hash to the entropy to
+  // make things easy when grabbing
+  // the checksum bits.
+  entropy = Buffer.concat([
+    this.entropy,
+    utils.sha256(this.entropy)
+  ]);
 
-  hash = utils.sha256(this.entropy);
-  bits = new bn(hash).toString(2);
-  while (bits.length % 256 !== 0)
-    bits = '0' + bits;
+  // Include the first `ENT / 32` bits
+  // of the hash (the checksum).
+  bits += bits / 32;
 
-  bin += bits.slice(0, (this.entropy.length * 8) / 32);
-
-  assert(bin.length % 11 === 0);
-
-  for (i = 0; i < bin.length / 11; i++) {
-    wi = parseInt(bin.slice(i * 11, (i + 1) * 11), 2);
-    mnemonic.push(wordlist[wi]);
+  // Build the mnemonic by reading
+  // 11 bit indexes from the entropy.
+  for (i = 0; i < bits; i++) {
+    i--;
+    word = 0;
+    for (j = 0; j < 11; j++) {
+      i++;
+      oct = i / 8 | 0;
+      bit = i % 8;
+      word <<= 1;
+      word |= (entropy[oct] >>> (7 - bit)) & 1;
+    }
+    mnemonic.push(wordlist[word]);
   }
 
-  if (this.lang === 'japanese')
+  // Japanese likes double-width spaces.
+  if (this.language === 'japanese')
     return mnemonic.join('\u3000');
 
   return mnemonic.join(' ');
@@ -184,12 +195,12 @@ Mnemonic.prototype.createMnemonic = function createMnemonic() {
 
 /**
  * Retrieve the wordlist for a language.
- * @param {String} lang
+ * @param {String} language
  * @returns {String[]}
  */
 
-Mnemonic.getWordlist = function getWordlist(lang) {
-  switch (lang) {
+Mnemonic.getWordlist = function getWordlist(language) {
+  switch (language) {
     case 'simplified chinese':
       return require('../../etc/chinese-simplified.js');
     case 'traditional chinese':
@@ -203,7 +214,7 @@ Mnemonic.getWordlist = function getWordlist(lang) {
     case 'japanese':
       return require('../../etc/japanese.js');
     default:
-      assert(false, 'Unknown language: ' + lang);
+      assert(false, 'Unknown language: ' + language);
   }
 };
 
@@ -656,7 +667,8 @@ HDPrivateKey.prototype.derivePath = function derivePath(path) {
 
 /**
  * Create an hd private key from a seed.
- * @param {Buffer|Mnemonic|Object} options - A buffer, HD seed, or HD seed options.
+ * @param {Buffer|Mnemonic|Object} options - A buffer,
+ * HD seed, or HD seed options.
  * @param {String?} networkType
  * @returns {Object} A "naked" key (a
  * plain javascript object which is suitable
diff --git a/test/mnemonic-test.js b/test/mnemonic-test.js
index fc52884e..92a39a70 100644
--- a/test/mnemonic-test.js
+++ b/test/mnemonic-test.js
@@ -13,7 +13,7 @@ describe('Mnemonic', function() {
     var xpriv = data[3];
     it('should create an english mnemonic (' + i + ')', function() {
       var mnemonic = new bcoin.hd.mnemonic({
-        lang: 'english',
+        language: 'english',
         entropy: entropy,
         passphrase: 'TREZOR'
       });
@@ -32,7 +32,7 @@ describe('Mnemonic', function() {
     var xpriv = data.bip32_xprv;
     it('should create a japanese mnemonic (' + i + ')', function() {
       var mnemonic = new bcoin.hd.mnemonic({
-        lang: 'japanese',
+        language: 'japanese',
         entropy: entropy,
         passphrase: passphrase
       });