diff --git a/lib/hdprivatekey.js b/lib/hdprivatekey.js
index ad53e1c..8d2d222 100644
--- a/lib/hdprivatekey.js
+++ b/lib/hdprivatekey.js
@@ -62,6 +62,22 @@ function HDPrivateKey(arg) {
   }
 }
 
+/**
+ * Verifies that a given path is valid.
+ *
+ * @param {string|number} arg
+ * @param {boolean?} hardened
+ * @return {boolean}
+ */
+HDPrivateKey.prototype.isValidPath = function(arg, hardened) {
+  try {
+    this.derive(arg, hardened);
+    return true;
+  } catch (err) {
+    return false;
+  }
+};
+
 /**
  * Get a derivated child based on a string or number.
  *
@@ -101,9 +117,15 @@ HDPrivateKey.prototype._deriveWithNumber = function(index, hardened) {
   if (index >= HDPrivateKey.Hardened) {
     hardened = true;
   }
+
   if (index < HDPrivateKey.Hardened && hardened) {
     index += HDPrivateKey.Hardened;
   }
+
+  if (index < 0 || index >= HDPrivateKey.MaxIndex) {
+    throw new hdErrors.InvalidPath(index);
+  }
+
   var cached = HDKeyCache.get(this.xprivkey, index, hardened);
   if (cached) {
     return cached;
@@ -443,6 +465,8 @@ HDPrivateKey.DefaultFingerprint = 0;
 HDPrivateKey.DefaultChildIndex = 0;
 HDPrivateKey.DefaultNetwork = Network.livenet;
 HDPrivateKey.Hardened = 0x80000000;
+HDPrivateKey.MaxIndex = 2 * HDPrivateKey.Hardened;
+
 HDPrivateKey.RootElementAlias = ['m', 'M', 'm\'', 'M\''];
 
 HDPrivateKey.VersionSize = 4;
diff --git a/lib/hdpublickey.js b/lib/hdpublickey.js
index 158aa05..979faf9 100644
--- a/lib/hdpublickey.js
+++ b/lib/hdpublickey.js
@@ -65,6 +65,22 @@ function HDPublicKey(arg) {
   }
 }
 
+
+/**
+ * Verifies that a given path is valid.
+ *
+ * @param {string|number} arg
+ * @return {boolean}
+ */
+HDPublicKey.prototype.isValidPath = function(arg) {
+  try {
+    this.derive(arg);
+    return true;
+  } catch (err) {
+    return false;
+  }
+};
+
 /**
  * Get a derivated child based on a string or number.
  *
@@ -86,11 +102,10 @@ function HDPublicKey(arg) {
  * ```
  *
  * @param {string|number} arg
- * @param {boolean?} hardened
  */
-HDPublicKey.prototype.derive = function (arg, hardened) {
+HDPublicKey.prototype.derive = function (arg) {
   if (_.isNumber(arg)) {
-    return this._deriveWithNumber(arg, hardened);
+    return this._deriveWithNumber(arg);
   } else if (_.isString(arg)) {
     return this._deriveFromString(arg);
   } else {
@@ -98,11 +113,14 @@ HDPublicKey.prototype.derive = function (arg, hardened) {
   }
 };
 
-HDPublicKey.prototype._deriveWithNumber = function (index, hardened) {
-  if (hardened || index >= HDPublicKey.Hardened) {
+HDPublicKey.prototype._deriveWithNumber = function (index) {
+  if (index >= HDPublicKey.Hardened) {
     throw new hdErrors.InvalidIndexCantDeriveHardened();
   }
-  var cached = HDKeyCache.get(this.xpubkey, index, hardened);
+  if (index < 0) {
+    throw new hdErrors.InvalidPath(index);
+  }
+  var cached = HDKeyCache.get(this.xpubkey, index, false);
   if (cached) {
     return cached;
   }
@@ -123,12 +141,16 @@ HDPublicKey.prototype._deriveWithNumber = function (index, hardened) {
     chainCode: chainCode,
     publicKey: publicKey
   });
-  HDKeyCache.set(this.xpubkey, index, hardened, derived);
+  HDKeyCache.set(this.xpubkey, index, false, derived);
   return derived;
 };
 
 HDPublicKey.prototype._deriveFromString = function (path) {
   /* jshint maxcomplexity: 8 */
+  if (_.contains(path, "'")) {
+    throw new hdErrors.InvalidIndexCantDeriveHardened();
+  }
+
   var steps = path.split('/');
 
   // Special cases:
@@ -143,8 +165,7 @@ HDPublicKey.prototype._deriveFromString = function (path) {
   var result = this;
   for (var step in steps) {
     var index = parseInt(steps[step]);
-    var hardened = steps[step] !== index.toString();
-    result = result._deriveWithNumber(index, hardened);
+    result = result._deriveWithNumber(index);
   }
   return result;
 };
diff --git a/test/hdprivatekey.js b/test/hdprivatekey.js
index 6ba3b4d..aec7563 100644
--- a/test/hdprivatekey.js
+++ b/test/hdprivatekey.js
@@ -190,6 +190,24 @@ describe('HDPrivate key interface', function() {
     derivedByNumber.xprivkey.should.equal(derivedByString.xprivkey);
   });
 
+  it('validates correct paths', function() {
+    var privateKey = new HDPrivateKey(xprivkey);
+    var valid = privateKey.isValidPath('m/0\'/1/2\'');
+    valid.should.equal(true);
+
+    var valid = privateKey.isValidPath(123, true);
+    valid.should.equal(true);
+  });
+
+  it('validates illigal paths', function() {
+    var privateKey = new HDPrivateKey(xprivkey);
+    var valid = privateKey.isValidPath('m/-1/12');
+    valid.should.equal(false);
+
+    var valid = privateKey.isValidPath(HDPrivateKey.MaxHardened);
+    valid.should.equal(false);
+  });
+
   describe('conversion to plain object/json', function() {
     var plainObject = {
       'network':'livenet',
diff --git a/test/hdpublickey.js b/test/hdpublickey.js
index 721fca8..be25b7b 100644
--- a/test/hdpublickey.js
+++ b/test/hdpublickey.js
@@ -216,10 +216,28 @@ describe('HDPublicKey interface', function() {
 
     it('can\'t derive hardened keys', function() {
       expectFail(function() {
-        return new HDPublicKey(xpubkey).derive(HDPublicKey.Hardened + 1);
+        return new HDPublicKey(xpubkey).derive(HDPublicKey.Hardened);
       }, hdErrors.InvalidDerivationArgument);
     });
 
+  it('validates correct paths', function() {
+    var publicKey = new HDPublicKey(xpubkey);
+    var valid = publicKey.isValidPath('m/123/12');
+    valid.should.equal(true);
+
+    var valid = publicKey.isValidPath(123, true);
+    valid.should.equal(true);
+  });
+
+  it('validates illigal paths', function() {
+    var publicKey = new HDPublicKey(xpubkey);
+    var valid = publicKey.isValidPath('m/-1/12');
+    valid.should.equal(false);
+
+    var valid = publicKey.isValidPath(HDPublicKey.Hardened);
+    valid.should.equal(false);
+  });
+
     it('should use the cache', function() {
       var pubkey = new HDPublicKey(xpubkey);
       var derived1 = pubkey.derive(0);