diff --git a/lib/privatekey.js b/lib/privatekey.js
index a16ef08..eaecd00 100644
--- a/lib/privatekey.js
+++ b/lib/privatekey.js
@@ -157,7 +157,7 @@ PrivateKey._transformBuffer = function(buf, network) {
   }
 
   if (network && info.network !== Networks.get(network)) {
-    throw TypeError('Private key network mismatch');
+    throw new TypeError('Private key network mismatch');
   }
 
   info.bn = BN.fromBuffer(buf.slice(1, 32 + 1));
diff --git a/test/privatekey.js b/test/privatekey.js
index e0dd4bd..6fe249d 100644
--- a/test/privatekey.js
+++ b/test/privatekey.js
@@ -90,7 +90,7 @@ describe('PrivateKey', function() {
   it('should not be able to instantiate private key WIF because of unknown network byte', function() {
     expect(function() {
       var buf = base58check.decode('L3T1s1TYP9oyhHpXgkyLoJFGniEgkv2Jhi138d7R2yJ9F4QdDU2m');
-      var buf2 = Buffer.concat([new Buffer(0x01, 'hex'), buf.slice(1, 33)]);
+      var buf2 = Buffer.concat([new Buffer('ff', 'hex'), buf.slice(1, 33)]);
       var a = new PrivateKey(buf2);
     }).to.throw('Invalid network');
   });