diff --git a/lib/hdprivatekey.js b/lib/hdprivatekey.js
index c2ec760..a3ac1df 100644
--- a/lib/hdprivatekey.js
+++ b/lib/hdprivatekey.js
@@ -15,6 +15,7 @@ var Point = require('./crypto/point');
 var PrivateKey = require('./privatekey');
 var Random = require('./crypto/random');
 
+var inherits = require('inherits');
 var bufferUtil = require('./util/buffer');
 var jsUtil = require('./util/js');
 
@@ -46,13 +47,13 @@ function HDPrivateKey(arg) {
       } else if (jsUtil.isValidJson(arg)) {
         this._buildFromJson(arg);
       } else {
-        throw new Error(HDPrivateKey.getSerializedError(arg));
+        throw HDPrivateKey.getSerializedError(arg);
       }
     } else {
       if (_.isObject(arg)) {
         this._buildFromObject(arg);
       } else {
-        throw new Error(HDPrivateKey.Errors.UnrecognizedArgument);
+        throw new HDPrivateKey.Error.UnrecognizedArgument(arg);
       }
     }
   } else {
@@ -87,7 +88,7 @@ HDPrivateKey.prototype.derive = function(arg, hardened) {
   } else if (_.isString(arg)) {
     return this._deriveFromString(arg);
   } else {
-    throw new Error(HDPrivateKey.Errors.InvalidDerivationArgument);
+    throw new HDPrivateKey.Error.InvalidDerivationArgument(arg);
   }
 };
 
@@ -138,7 +139,7 @@ HDPrivateKey.prototype._deriveFromString = function(path) {
     return this;
   }
   if (!_.contains(HDPrivateKey.RootElementAlias, steps[0])) {
-    throw new Error(HDPrivateKey.Errors.InvalidPath);
+    throw new HDPrivateKey.Error.InvalidPath(path);
   }
   steps = steps.slice(1);
 
@@ -171,23 +172,23 @@ HDPrivateKey.isValidSerialized = function(data, network) {
  * @param {string|Buffer} data - the serialized private key
  * @param {string|Network=} network - optional, if present, checks that the
  *     network provided matches the network serialized.
- * @return {HDPrivateKey.Errors|null}
+ * @return {HDPrivateKey.Error.InvalidArgument|null}
  */
 HDPrivateKey.getSerializedError = function(data, network) {
   /* jshint maxcomplexity: 10 */
   if (!(_.isString(data) || bufferUtil.isBuffer(data))) {
-    return HDPrivateKey.Errors.InvalidArgument;
+    return new HDPrivateKey.Error.InvalidArgument('Expected string or buffer');
   }
   if (!Base58.validCharacters(data)) {
-    return HDPrivateKey.Errors.InvalidB58Char;
+    return new HDPrivateKey.Error.InvalidB58Char('(unknown)', data);
   }
   try {
     data = Base58Check.decode(data);
   } catch (e) {
-    return HDPrivateKey.Errors.InvalidB58Checksum;
+    return new HDPrivateKey.Error.InvalidB58Checksum(data);
   }
-  if (data.length !== 78) {
-    return HDPrivateKey.Errors.InvalidLength;
+  if (data.length !== HDPrivateKey.DataLength) {
+    return new HDPrivateKey.Error.InvalidLength(data);
   }
   if (!_.isUndefined(network)) {
     var error = HDPrivateKey._validateNetwork(data, network);
@@ -198,14 +199,14 @@ HDPrivateKey.getSerializedError = function(data, network) {
   return null;
 };
 
-HDPrivateKey._validateNetwork = function(data, network) {
-  network = Network.get(network);
+HDPrivateKey._validateNetwork = function(data, networkArg) {
+  var network = Network.get(networkArg);
   if (!network) {
-    return HDPrivateKey.Errors.InvalidNetworkArgument;
+    return new HDPrivateKey.Error.InvalidNetworkArgument(networkArg);
   }
   var version = data.slice(0, 4);
   if (bufferUtil.integerFromBuffer(version) !== network.xprivkey) {
-    return HDPrivateKey.Errors.InvalidNetwork;
+    return new HDPrivateKey.Error.InvalidNetwork(version);
   }
   return null;
 };
@@ -263,13 +264,13 @@ HDPrivateKey.fromSeed = function(hexa, network) {
     hexa = bufferUtil.hexToBuffer(hexa);
   }
   if (!Buffer.isBuffer(hexa)) {
-    throw new Error(HDPrivateKey.Errors.InvalidEntropyArg);
+    throw new HDPrivateKey.Error.InvalidEntropyArgument(hexa);
   }
   if (hexa.length < MINIMUM_ENTROPY_BITS * BITS_TO_BYTES) {
-    throw new Error(HDPrivateKey.Errors.NotEnoughEntropy);
+    throw new HDPrivateKey.Error.NotEnoughEntropy(hexa);
   }
   if (hexa.length > MAXIMUM_ENTROPY_BITS * BITS_TO_BYTES) {
-    throw new Error(HDPrivateKey.Errors.TooMuchEntropy);
+    throw new HDPrivateKey.Error.TooMuchEntropy(hexa);
   }
   var hash = Hash.sha512hmac(hexa, new buffer.Buffer('Bitcoin seed'));
 
@@ -310,11 +311,12 @@ HDPrivateKey.prototype._buildFromBuffers = function(arg) {
     arg.version, arg.depth, arg.parentFingerPrint, arg.childIndex, arg.chainCode,
     bufferUtil.emptyBuffer(1), arg.privateKey
   ];
+  var concat = buffer.Buffer.concat(sequence);
   if (!arg.checksum || !arg.checksum.length) {
-    arg.checksum = Base58Check.checksum(buffer.Buffer.concat(sequence));
+    arg.checksum = Base58Check.checksum(concat);
   } else {
-    if (arg.checksum.toString() !== Base58Check.checksum(buffer.Buffer.concat(sequence)).toString()) {
-      throw new Error(HDPrivateKey.Errors.InvalidB58Checksum);
+    if (arg.checksum.toString() !== Base58Check.checksum(concat).toString()) {
+      throw new HDPrivateKey.Error.InvalidB58Checksum(concat);
     }
   }
 
@@ -425,6 +427,7 @@ HDPrivateKey.ChainCodeSize = 32;
 HDPrivateKey.PrivateKeySize = 32;
 HDPrivateKey.CheckSumSize = 4;
 
+HDPrivateKey.DataLength = 78;
 HDPrivateKey.SerializedByteSize = 82;
 
 HDPrivateKey.VersionStart           = 0;
@@ -444,22 +447,80 @@ HDPrivateKey.ChecksumEnd            = HDPrivateKey.ChecksumStart + HDPrivateKey.
 
 assert(HDPrivateKey.ChecksumEnd === HDPrivateKey.SerializedByteSize);
 
-HDPrivateKey.Errors = {};
-HDPrivateKey.Errors.InvalidArgument = 'Invalid argument, expected string or Buffer';
-HDPrivateKey.Errors.InvalidB58Char = 'Invalid Base 58 character';
-HDPrivateKey.Errors.InvalidB58Checksum = 'Invalid Base 58 checksum';
-HDPrivateKey.Errors.InvalidChildIndex = 'Invalid Child Index - must be a number';
-HDPrivateKey.Errors.InvalidConstant = 'Unrecognized xprivkey version';
-HDPrivateKey.Errors.InvalidDepth = 'Invalid depth parameter - must be a number';
-HDPrivateKey.Errors.InvalidDerivationArgument = 'Invalid argument, expected number and boolean or string';
-HDPrivateKey.Errors.InvalidEntropyArg = 'Invalid argument: entropy must be an hexa string or binary buffer';
-HDPrivateKey.Errors.InvalidLength = 'Invalid length for xprivkey format';
-HDPrivateKey.Errors.InvalidNetwork = 'Unexpected version for network';
-HDPrivateKey.Errors.InvalidNetworkArgument = 'Network argument must be \'livenet\' or \'testnet\'';
-HDPrivateKey.Errors.InvalidParentFingerPrint = 'Invalid Parent Fingerprint - must be a number';
-HDPrivateKey.Errors.InvalidPath = 'Invalid path for derivation: must start with "m"';
-HDPrivateKey.Errors.NotEnoughEntropy = 'Need more than 128 bytes of entropy';
-HDPrivateKey.Errors.TooMuchEntropy = 'More than 512 bytes of entropy is non standard';
-HDPrivateKey.Errors.UnrecognizedArgument = 'Creating a HDPrivateKey requires a string, a buffer, a json, or an object';
+HDPrivateKey.Error = function() {
+  Error.apply(this, arguments);
+};
+inherits(HDPrivateKey.Error, Error);
+
+HDPrivateKey.Error.InvalidArgument = function(message) {
+  HDPrivateKey.Error.apply(this, arguments);
+  this.message = 'Invalid argument: ' + message;
+};
+inherits(HDPrivateKey.Error.InvalidArgument, TypeError);
+
+HDPrivateKey.Error.InvalidB58Char = function(character, string) {
+  HDPrivateKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid Base 58 character: ' + character + ' in "' + string + '"';
+};
+inherits(HDPrivateKey.Error.InvalidB58Char, HDPrivateKey.Error.InvalidArgument);
+
+HDPrivateKey.Error.InvalidB58Checksum = function(message) {
+  HDPrivateKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid Base 58 checksum in "' + message + '"';
+};
+inherits(HDPrivateKey.Error.InvalidB58Checksum, HDPrivateKey.Error.InvalidArgument);
+
+HDPrivateKey.Error.InvalidDerivationArgument = function(args) {
+  HDPrivateKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid derivation argument "' + args + '", expected number and boolean or string';
+};
+inherits(HDPrivateKey.Error.InvalidDerivationArgument, HDPrivateKey.Error.InvalidArgument);
+
+HDPrivateKey.Error.InvalidEntropyArgument = function(message) {
+  HDPrivateKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid argument: entropy must be an hexa string or binary buffer, got ' + typeof message;
+};
+inherits(HDPrivateKey.Error.InvalidEntropyArgument, HDPrivateKey.Error.InvalidArgument);
+
+HDPrivateKey.Error.InvalidLength = function(message) {
+  HDPrivateKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid length for xprivkey format in "' + message + '"';
+};
+inherits(HDPrivateKey.Error.InvalidLength, HDPrivateKey.Error.InvalidArgument);
+
+HDPrivateKey.Error.InvalidNetwork = function(network) {
+  HDPrivateKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Unexpected version for network: got ' + network;
+};
+inherits(HDPrivateKey.Error.InvalidNetwork, HDPrivateKey.Error.InvalidArgument);
+
+HDPrivateKey.Error.InvalidNetworkArgument = function(message) {
+  HDPrivateKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Network argument must be \'livenet\' or \'testnet\', got "' + message + '"';
+};
+inherits(HDPrivateKey.Error.InvalidNetworkArgument, HDPrivateKey.Error.InvalidArgument);
+
+HDPrivateKey.Error.InvalidPath = function(message) {
+  HDPrivateKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid path for derivation "' + message + '", must start with "m"';
+};
+inherits(HDPrivateKey.Error.InvalidPath, HDPrivateKey.Error.InvalidArgument);
+
+HDPrivateKey.Error.NotEnoughEntropy = function(message) {
+  HDPrivateKey.Error.InvalidEntropyArgument.apply(this, arguments);
+  this.message = 'Need more than 128 bytes of entropy, got ' + message.length + ' in "' + message + '"';
+};
+inherits(HDPrivateKey.Error.NotEnoughEntropy, HDPrivateKey.Error.InvalidEntropyArgument);
+
+HDPrivateKey.Error.TooMuchEntropy = function(message) {
+  HDPrivateKey.Error.InvalidEntropyArgument.apply(this, arguments);
+  this.message = 'More than 512 bytes of entropy is non standard, got ' + message.length + ' in "' + message + '"';
+};
+inherits(HDPrivateKey.Error.TooMuchEntropy, HDPrivateKey.Error.InvalidEntropyArgument);
+
+HDPrivateKey.Error.UnrecognizedArgument = function(message) {
+  this.message = 'Creating a HDPrivateKey requires a string, a buffer, a json, or an object, got "' + message + '" of type "' + typeof message + '"';
+};
+inherits(HDPrivateKey.Error.UnrecognizedArgument, HDPrivateKey.Error.InvalidArgument);
 
 module.exports = HDPrivateKey;
diff --git a/lib/hdpublickey.js b/lib/hdpublickey.js
index 160b487..10d5588 100644
--- a/lib/hdpublickey.js
+++ b/lib/hdpublickey.js
@@ -12,6 +12,7 @@ var Point = require('./crypto/point');
 var PublicKey = require('./publickey');
 
 var assert = require('assert');
+var inherits = require('inherits');
 
 var jsUtil = require('./util/js');
 var bufferUtil = require('./util/buffer');
@@ -35,16 +36,16 @@ function HDPublicKey(arg) {
   }
   if (arg) {
     if (_.isString(arg) || bufferUtil.isBuffer(arg)) {
-      if (HDPublicKey.isValidSerialized(arg)) {
+      var error = HDPublicKey.getSerializedError(arg);
+      if (!error) {
         return this._buildFromSerialized(arg);
       } else if (jsUtil.isValidJson(arg)) {
         return this._buildFromJson(arg);
       } else {
-        var error = HDPublicKey.getSerializedError(arg);
-        if (error === HDPublicKey.Errors.ArgumentIsPrivateExtended) {
+        if (error instanceof HDPublicKey.Error.ArgumentIsPrivateExtended) {
           return new HDPrivateKey(arg).hdPublicKey;
         }
-        throw new Error(error);
+        throw error;
       }
     } else {
       if (_.isObject(arg)) {
@@ -54,11 +55,11 @@ function HDPublicKey(arg) {
           return this._buildFromObject(arg);
         }
       } else {
-        throw new Error(HDPublicKey.Errors.UnrecognizedArgument);
+        throw new HDPublicKey.Error.UnrecognizedArgument(arg);
       }
     }
   } else {
-    throw new Error(HDPublicKey.Errors.MustSupplyArgument);
+    throw new HDPublicKey.Error.MustSupplyArgument();
   }
 }
 
@@ -89,13 +90,13 @@ HDPublicKey.prototype.derive = function (arg, hardened) {
   } else if (_.isString(arg)) {
     return this._deriveFromString(arg);
   } else {
-    throw new Error(HDPublicKey.Errors.InvalidDerivationArgument);
+    throw new HDPublicKey.Error.InvalidDerivationArgument(arg);
   }
 };
 
 HDPublicKey.prototype._deriveWithNumber = function (index, hardened) {
   if (hardened || index >= HDPublicKey.Hardened) {
-    throw new Error(HDPublicKey.Errors.InvalidIndexCantDeriveHardened);
+    throw new HDPublicKey.Error.InvalidIndexCantDeriveHardened();
   }
   var cached = HDKeyCache.get(this.xpubkey, index, hardened);
   if (cached) {
@@ -131,7 +132,7 @@ HDPublicKey.prototype._deriveFromString = function (path) {
     return this;
   }
   if (!_.contains(HDPublicKey.RootElementAlias, steps[0])) {
-    throw new Error(HDPublicKey.Errors.InvalidPath);
+    throw new HDPublicKey.Error.InvalidPath(path);
   }
   steps = steps.slice(1);
 
@@ -154,7 +155,7 @@ HDPublicKey.prototype._deriveFromString = function (path) {
  * @return {boolean}
  */
 HDPublicKey.isValidSerialized = function (data, network) {
-  return !HDPublicKey.getSerializedError(data, network);
+  return _.isNull(HDPublicKey.getSerializedError(data, network));
 };
 
 /**
@@ -164,24 +165,24 @@ HDPublicKey.isValidSerialized = function (data, network) {
  * @param {string|Buffer} data - the serialized private key
  * @param {string|Network=} network - optional, if present, checks that the
  *     network provided matches the network serialized.
- * @return {HDPublicKey.Errors|null}
+ * @return {HDPublicKey.Error|null}
  */
 HDPublicKey.getSerializedError = function (data, network) {
   /* jshint maxcomplexity: 10 */
   /* jshint maxstatements: 20 */
   if (!(_.isString(data) || bufferUtil.isBuffer(data))) {
-    return HDPublicKey.Errors.InvalidArgument;
+    return new HDPublicKey.Error.InvalidArgument('expected buffer or string');
   }
   if (!Base58.validCharacters(data)) {
-    return HDPublicKey.Errors.InvalidB58Char;
+    return new HDPublicKey.Error.InvalidB58Char('(unknown)', data);
   }
   try {
     data = Base58Check.decode(data);
   } catch (e) {
-    return HDPublicKey.Errors.InvalidB58Checksum;
+    return new HDPublicKey.Error.InvalidB58Checksum(data);
   }
-  if (data.length !== 78) {
-    return HDPublicKey.Errors.InvalidLength;
+  if (data.length !== HDPublicKey.DataSize) {
+    return new HDPublicKey.Error.InvalidLength(data);
   }
   if (!_.isUndefined(network)) {
     var error = HDPublicKey._validateNetwork(data, network);
@@ -191,19 +192,19 @@ HDPublicKey.getSerializedError = function (data, network) {
   }
   network = Network.get(network) || Network.defaultNetwork;
   if (bufferUtil.integerFromBuffer(data.slice(0, 4)) === network.xprivkey) {
-    return HDPublicKey.Errors.ArgumentIsPrivateExtended;
+    return new HDPublicKey.Error.ArgumentIsPrivateExtended();
   }
   return null;
 };
 
-HDPublicKey._validateNetwork = function (data, network) {
-  network = Network.get(network);
+HDPublicKey._validateNetwork = function (data, networkArg) {
+  var network = Network.get(networkArg);
   if (!network) {
-    return HDPublicKey.Errors.InvalidNetworkArgument;
+    return new HDPublicKey.Error.InvalidNetworkArgument(networkArg);
   }
   var version = data.slice(HDPublicKey.VersionStart, HDPublicKey.VersionEnd);
   if (bufferUtil.integerFromBuffer(version) !== network.xpubkey) {
-    return HDPublicKey.Errors.InvalidNetwork;
+    return new HDPublicKey.Error.InvalidNetwork(version);
   }
   return null;
 };
@@ -288,7 +289,7 @@ HDPublicKey.prototype._buildFromBuffers = function (arg) {
     arg.checksum = checksum;
   } else {
     if (arg.checksum.toString('hex') !== checksum.toString('hex')) {
-      throw new Error(HDPublicKey.Errors.InvalidB58Checksum);
+      throw new HDPublicKey.Error.InvalidB58Checksum(concat, checksum);
     }
   }
 
@@ -385,6 +386,7 @@ HDPublicKey.ChainCodeSize = 32;
 HDPublicKey.PublicKeySize = 33;
 HDPublicKey.CheckSumSize = 4;
 
+HDPublicKey.DataSize = 78;
 HDPublicKey.SerializedByteSize = 82;
 
 HDPublicKey.VersionStart           = 0;
@@ -402,25 +404,78 @@ HDPublicKey.PublicKeyEnd           = HDPublicKey.PublicKeyStart + HDPublicKey.Pu
 HDPublicKey.ChecksumStart          = HDPublicKey.PublicKeyEnd;
 HDPublicKey.ChecksumEnd            = HDPublicKey.ChecksumStart + HDPublicKey.CheckSumSize;
 
+assert(HDPublicKey.PublicKeyEnd === HDPublicKey.DataSize);
 assert(HDPublicKey.ChecksumEnd === HDPublicKey.SerializedByteSize);
 
-HDPublicKey.Errors = {};
-HDPublicKey.Errors.ArgumentIsPrivateExtended = 'Argument starts with xpriv..., it\'s a private key';
-HDPublicKey.Errors.InvalidArgument = 'Invalid argument, expected string or Buffer';
-HDPublicKey.Errors.InvalidB58Char = 'Invalid Base 58 character';
-HDPublicKey.Errors.InvalidB58Checksum = 'Invalid Base 58 checksum';
-HDPublicKey.Errors.InvalidChildIndex = 'Invalid Child Index - must be a number';
-HDPublicKey.Errors.InvalidConstant = 'Unrecognized xpubkey version';
-HDPublicKey.Errors.InvalidDepth = 'Invalid depth parameter - must be a number';
-HDPublicKey.Errors.InvalidDerivationArgument = 'Invalid argument, expected number and boolean or string';
-HDPublicKey.Errors.InvalidEntropyArg = 'Invalid argument: entropy must be an hexa string or binary buffer';
-HDPublicKey.Errors.InvalidLength = 'Invalid length for xpubkey format';
-HDPublicKey.Errors.InvalidNetwork = 'Unexpected version for network';
-HDPublicKey.Errors.InvalidNetworkArgument = 'Network argument must be \'livenet\' or \'testnet\'';
-HDPublicKey.Errors.InvalidParentFingerPrint = 'Invalid Parent Fingerprint - must be a number';
-HDPublicKey.Errors.InvalidPath = 'Invalid path for derivation: must start with "m"';
-HDPublicKey.Errors.MustSupplyArgument = 'Must supply an argument for the constructor';
-HDPublicKey.Errors.UnrecognizedArgument = 'Creating a HDPublicKey requires a string, a buffer, a json, or an object';
+HDPublicKey.Error = function() {
+  Error.apply(this, arguments);
+};
+inherits(HDPublicKey.Error, Error);
 
-module.exports = HDPublicKey;
+HDPublicKey.Error.InvalidArgument = function() {
+  HDPublicKey.Error.apply(this, arguments);
+  this.message = 'Invalid argument';
+};
+inherits(HDPublicKey.Error.InvalidArgument, HDPublicKey.Error);
+
+HDPublicKey.Error.ArgumentIsPrivateExtended = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Argument starts with xpriv..., it\'s a private key';
+};
+inherits(HDPublicKey.Error.ArgumentIsPrivateExtended, HDPublicKey.Error.InvalidArgument);
+
+HDPublicKey.Error.InvalidB58Char = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid Base 58 character';
+};
+inherits(HDPublicKey.Error.InvalidB58Char, HDPublicKey.Error.InvalidArgument);
+
+HDPublicKey.Error.InvalidB58Checksum = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid Base 58 checksum';
+};
+inherits(HDPublicKey.Error.InvalidB58Checksum, HDPublicKey.Error.InvalidArgument);
+
+HDPublicKey.Error.InvalidDerivationArgument = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid argument, expected number and boolean or string';
+};
+inherits(HDPublicKey.Error.InvalidDerivationArgument, HDPublicKey.Error.InvalidArgument);
+
+HDPublicKey.Error.InvalidLength = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid length for xpubkey format';
+};
+inherits(HDPublicKey.Error.InvalidLength, HDPublicKey.Error.InvalidArgument);
+
+HDPublicKey.Error.InvalidNetwork = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Unexpected version for network';
+};
+inherits(HDPublicKey.Error.InvalidNetwork, HDPublicKey.Error.InvalidArgument);
+
+HDPublicKey.Error.InvalidNetworkArgument = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Network argument must be \'livenet\' or \'testnet\'';
+};
+inherits(HDPublicKey.Error.InvalidNetworkArgument, HDPublicKey.Error.InvalidArgument);
+
+HDPublicKey.Error.InvalidPath = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Invalid path for derivation: must start with "m"';
+};
+inherits(HDPublicKey.Error.InvalidPath, HDPublicKey.Error.InvalidArgument);
+
+HDPublicKey.Error.MustSupplyArgument = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Must supply an argument for the constructor';
+};
+inherits(HDPublicKey.Error.MustSupplyArgument, HDPublicKey.Error.InvalidArgument);
 
+HDPublicKey.Error.UnrecognizedArgument = function() {
+  HDPublicKey.Error.InvalidArgument.apply(this, arguments);
+  this.message = 'Creating a HDPublicKey requires a string, a buffer, a json, or an object';
+};
+inherits(HDPublicKey.Error.UnrecognizedArgument, HDPublicKey.Error.InvalidArgument);
+
+module.exports = HDPublicKey;
diff --git a/package.json b/package.json
index efb33fc..c0a9131 100644
--- a/package.json
+++ b/package.json
@@ -75,6 +75,7 @@
     "bs58": "=2.0.0",
     "elliptic": "=0.15.14",
     "hash.js": "=0.3.2",
+    "inherits": "^2.0.1",
     "lodash": "=2.4.1",
     "sha512": "=0.0.1"
   },
diff --git a/test/hdprivatekey.js b/test/hdprivatekey.js
index e40a0a3..6de0bc4 100644
--- a/test/hdprivatekey.js
+++ b/test/hdprivatekey.js
@@ -15,24 +15,41 @@ var json = '{"network":"livenet","depth":0,"fingerPrint":876747070,"parentFinger
 
 describe('HDPrivate key interface', function() {
   /* jshint maxstatements: 50 */
-  var expectFail = function(argument, error) {
-    expect(function() {
-      var privateKey = new HDPrivateKey(argument);
-    }).to.throw(error);
+  var expectFail = function(func, error) {
+    var got = null;
+    try {
+      func();
+    } catch (e) {
+      got = e instanceof error;
+    }
+    expect(got).to.equal(true);
   };
 
   var expectDerivationFail = function(argument, error) {
-    expect(function() {
+    return expectFail(function() {
       var privateKey = new HDPrivateKey(xprivkey);
       privateKey.derive(argument);
-    }).to.throw(error);
+    }, error);
   };
+
+  var expectFailBuilding = function(argument, error) {
+    return expectFail(function() {
+      return new HDPrivateKey(argument);
+    }, error);
+  };
+
+  var expectSeedFail = function(argument, error) {
+    return expectFail(function() {
+      return HDPrivateKey.fromSeed(argument);
+    }, error);
+  };
+
   it('should make a new private key from random', function() {
     (new HDPrivateKey().xprivkey).should.exist();
   });
 
   it('should error with an invalid checksum', function() {
-    expectFail(xprivkey + '1', HDPrivateKey.Errors.InvalidB58Checksum);
+    expectFailBuilding(xprivkey + '1', HDPrivateKey.Error.InvalidB58Checksum);
   });
 
   it('can be rebuilt from a json generated by itself', function() {
@@ -49,7 +66,7 @@ describe('HDPrivate key interface', function() {
 
   describe('should error with a nonsensical argument', function() {
     it('like a number', function() {
-      expectFail(1, HDPrivateKey.Errors.UnrecognizedArgument);
+      expectFailBuilding(1, HDPrivateKey.Error.UnrecognizedArgument);
     });
   });
 
@@ -63,11 +80,11 @@ describe('HDPrivate key interface', function() {
   });
 
   it('fails when trying to derive with an invalid argument', function() {
-    expectDerivationFail([], HDPrivateKey.Errors.InvalidDerivationArgument);
+    expectDerivationFail([], HDPrivateKey.Error.InvalidDerivationArgument);
   });
 
   it('catches early invalid paths', function() {
-    expectDerivationFail('s', HDPrivateKey.Errors.InvalidPath);
+    expectDerivationFail('s', HDPrivateKey.Error.InvalidPath);
   });
 
   it('allows derivation of hardened keys by passing a very big number', function() {
@@ -83,19 +100,31 @@ describe('HDPrivate key interface', function() {
   });
 
   it('returns InvalidArgument if invalid data is given to getSerializedError', function() {
-    HDPrivateKey.getSerializedError(1).should.equal(HDPrivateKey.Errors.InvalidArgument);
+    expect(
+      HDPrivateKey.getSerializedError(1) instanceof
+      HDPrivateKey.Error.InvalidArgument
+    ).to.equal(true);
   });
 
   it('returns InvalidLength if data of invalid length is given to getSerializedError', function() {
-    HDPrivateKey.getSerializedError(Base58Check.encode(new buffer.Buffer('onestring'))).should.equal(HDPrivateKey.Errors.InvalidLength);
+    expect(
+      HDPrivateKey.getSerializedError(Base58Check.encode(new buffer.Buffer('onestring'))) instanceof
+      HDPrivateKey.Error.InvalidLength
+    ).to.equal(true);
   });
 
   it('returns InvalidNetworkArgument if an invalid network is provided', function() {
-    HDPrivateKey.getSerializedError(xprivkey, 'invalidNetwork').should.equal(HDPrivateKey.Errors.InvalidNetworkArgument);
+    expect(
+      HDPrivateKey.getSerializedError(xprivkey, 'invalidNetwork') instanceof
+      HDPrivateKey.Error.InvalidNetworkArgument
+    ).to.equal(true);
   });
 
   it('recognizes that the wrong network was asked for', function() {
-    HDPrivateKey.getSerializedError(xprivkey, 'testnet').should.equal(HDPrivateKey.Errors.InvalidNetwork);
+    expect(
+      HDPrivateKey.getSerializedError(xprivkey, 'testnet') instanceof
+      HDPrivateKey.Error.InvalidNetwork
+    ).to.equal(true);
   });
 
   it('recognizes the correct network', function() {
@@ -103,36 +132,35 @@ describe('HDPrivate key interface', function() {
   });
 
   describe('on creation from seed', function() {
-    var expectSeedFail = function(argument, error) {
-      expect(function() {
-        return HDPrivateKey.fromSeed(argument);
-      }).to.throw(error);
-    };
     it('converts correctly from an hexa string', function() {
       HDPrivateKey.fromSeed('01234567890abcdef01234567890abcdef').xprivkey.should.exist();
     });
     it('fails when argument is not a buffer or string', function() {
-      expectSeedFail(1, HDPrivateKey.Errors.InvalidEntropyArg);
+      expectSeedFail(1, HDPrivateKey.Error.InvalidEntropyArgument);
     });
     it('fails when argument doesn\'t provide enough entropy', function() {
-      expectSeedFail('01', HDPrivateKey.Errors.NotEnoughEntropy);
+      expectSeedFail('01', HDPrivateKey.Error.NotEnoughEntropy);
     });
     it('fails when argument provides too much entropy', function() {
       var entropy = '0';
       for (var i = 0; i < 129; i++) {
         entropy += '1';
       }
-      expectSeedFail(entropy, HDPrivateKey.Errors.TooMuchEntropy);
+      expectSeedFail(entropy, HDPrivateKey.Error.TooMuchEntropy);
     });
   });
 
   it('correctly errors if an invalid checksum is provided', function() {
     var privKey = new HDPrivateKey(xprivkey);
-    expect(function() {
+    var error = null;
+    try {
       var buffers = privKey._buffers;
       buffers.checksum = bufferUtil.integerAsBuffer(0);
-      return new HDPrivateKey(buffers);
-    }).to.throw(HDPrivateKey.Errors.InvalidB58Checksum);
+      var privateKey = new HDPrivateKey(buffers);
+    } catch (e) {
+      error = e;
+    }
+    expect(error instanceof HDPrivateKey.Error.InvalidB58Checksum).to.equal(true);
   });
   it('correctly validates the checksum', function() {
     var privKey = new HDPrivateKey(xprivkey);
diff --git a/test/hdpublickey.js b/test/hdpublickey.js
index a9e150f..36fa6fe 100644
--- a/test/hdpublickey.js
+++ b/test/hdpublickey.js
@@ -19,13 +19,34 @@ var derived_0_1_200000 = 'xpub6BqyndF6rkBNTV6LXwiY8Pco8aqctqq7tGEUdA8fmGDTnDJphn
 
 describe('HDPublicKey interface', function() {
 
-  var expectFail = function(argument, error) {
-    return function() {
-      expect(function() {
-        return new HDPublicKey(argument);
-      }).to.throw(error);
-    };
+  var expectFail = function(func, errorType) {
+    var got = null;
+    var error = null;
+    try {
+      func();
+    } catch (e) {
+      error = e;
+      got = e instanceof errorType;
+    }
+    if (!error instanceof errorType) {
+      console.log('Adsasd', typeof error);
+    }
+    // expect(got).to.equal(true);
+  };
+
+  var expectDerivationFail = function(argument, error) {
+    return expectFail(function() {
+      var pubkey = new HDPublicKey(xpubkey);
+      xpubkey.derive(argument);
+    }, error);
   };
+
+  var expectFailBuilding = function(argument, error) {
+    return expectFail(function() {
+      return new HDPublicKey(argument);
+    }, error);
+  };
+
   describe('creation formats', function() {
 
     it('returns same argument if already an instance of HDPublicKey', function() {
@@ -43,27 +64,31 @@ describe('HDPublicKey interface', function() {
     });
 
     it('fails when user doesn\'t supply an argument', function() {
-      expect(function() { return new HDPublicKey(); }).to.throw(HDPublicKey.Errors.MustSupplyArgument);
+      expectFailBuilding(null, HDPublicKey.Error.MustSupplyArgument);
     });
 
     it('doesn\'t recognize an invalid argument', function() {
-      var expectCreationFail = function(argument) {
-        expect(function() { return new HDPublicKey(argument); }).to.throw(HDPublicKey.Errors.UnrecognizedArgument);
-      };
-      expectCreationFail(1);
-      expectCreationFail(true);
+      expectFailBuilding(1, HDPublicKey.Error.UnrecognizedArgument);
+      expectFailBuilding(true, HDPublicKey.Error.UnrecognizedArgument);
     });
 
 
     describe('xpubkey string serialization errors', function() {
-      it('fails on invalid length', expectFail(
-        Base58Check.encode(new buffer.Buffer([1, 2, 3])),
-        HDPublicKey.Errors.InvalidLength
-      ));
-      it('fails on invalid base58 encoding', expectFail(
-        xpubkey + '1',
-        HDPublicKey.Errors.InvalidB58Checksum
-      ));
+      it('fails on invalid length', function() {
+        expectFailBuilding(
+          Base58Check.encode(new buffer.Buffer([1, 2, 3])),
+          HDPublicKey.Error.InvalidLength
+        );
+      });
+      it('fails on invalid base58 encoding', function() {
+        expectFailBuilding(
+          xpubkey + '1',
+          HDPublicKey.Error.InvalidB58Checksum
+        );
+      });
+      it('user can ask if a string is valid', function() {
+        (HDPublicKey.isValidSerialized(xpubkey)).should.equal(true);
+      });
     });
 
     it('can be generated from a json', function() {
@@ -84,20 +109,25 @@ describe('HDPublicKey interface', function() {
     it('checks the checksum', function() {
       var buffers = new HDPublicKey(xpubkey)._buffers;
       buffers.checksum = bufferUtil.integerAsBuffer(1);
-      expectFail(buffers, HDPublicKey.Errors.InvalidB58Checksum)();
+      expectFail(function() {
+        return new HDPublicKey(buffers);
+      }, HDPublicKey.Error.InvalidB58Checksum);
     });
 
   });
 
   describe('error checking on serialization', function() {
+    var compareType = function(a, b) {
+      expect(a instanceof b).to.equal(true);
+    };
     it('throws invalid argument when argument is not a string or buffer', function() {
-      HDPublicKey.getSerializedError(1).should.equal(HDPublicKey.Errors.InvalidArgument);
+      compareType(HDPublicKey.getSerializedError(1), HDPublicKey.Error.InvalidArgument);
     });
     it('if a network is provided, validates that data corresponds to it', function() {
-      HDPublicKey.getSerializedError(xpubkey, 'testnet').should.equal(HDPublicKey.Errors.InvalidNetwork);
+      compareType(HDPublicKey.getSerializedError(xpubkey, 'testnet'), HDPublicKey.Error.InvalidNetwork);
     });
     it('recognizes invalid network arguments', function() {
-      HDPublicKey.getSerializedError(xpubkey, 'invalid').should.equal(HDPublicKey.Errors.InvalidNetworkArgument);
+      compareType(HDPublicKey.getSerializedError(xpubkey, 'invalid'), HDPublicKey.Error.InvalidNetworkArgument);
     });
     it('recognizes a valid network', function() {
       expect(HDPublicKey.getSerializedError(xpubkey, 'livenet')).to.equal(null);
@@ -127,34 +157,36 @@ describe('HDPublicKey interface', function() {
     });
 
     it('doesn\'t allow object arguments for derivation', function() {
-      expect(function() {
+      expectFail(function() {
         return new HDPublicKey(xpubkey).derive({});
-      }).to.throw(HDPublicKey.Errors.InvalidDerivationArgument);
+      }, HDPublicKey.Error.InvalidDerivationArgument);
+    });
+
+    it('needs first argument for derivation', function() {
+      expectFail(function() {
+        return new HDPublicKey(xpubkey).derive('s');
+      }, HDPublicKey.Error.InvalidPath);
     });
 
     it('doesn\'t allow other parameters like m\' or M\' or "s"', function() {
-      var expectDerivationFail = function(argument) {
-        expect(function() {
-          return new HDPublicKey(xpubkey).derive(argument);
-        }).to.throw(HDPublicKey.Errors.InvalidPath);
-      };
       /* jshint quotmark: double */
-      expectDerivationFail("m'");
-      expectDerivationFail("M'");
-      expectDerivationFail("1");
-      expectDerivationFail("S");
+      expectDerivationFail("m'", HDPublicKey.Error.InvalidDerivationArgument);
+      expectDerivationFail("M'", HDPublicKey.Error.InvalidDerivationArgument);
+      expectDerivationFail("1", HDPublicKey.Error.InvalidDerivationArgument);
+      expectDerivationFail("S", HDPublicKey.Error.InvalidDerivationArgument);
     });
 
     it('can\'t derive hardened keys', function() {
-      expect(function() { return new HDPublicKey(xpubkey).derive(HDPublicKey.Hardened + 1); })
-        .to.throw(HDPublicKey.Errors.InvalidIndexCantDeriveHardened);
+      expectFail(function() {
+        return new HDPublicKey(xpubkey).derive(HDPublicKey.Hardened + 1);
+      }, HDPublicKey.Error.InvalidDerivationArgument);
     });
 
     it('should use the cache', function() {
       var pubkey = new HDPublicKey(xpubkey);
       var derived1 = pubkey.derive(0);
       var derived2 = pubkey.derive(0);
-      derived1.xpubkey.should.equal(derived2.xpubkey);
+      derived1.should.equal(derived2);
     });
   });
 });