diff --git a/lib/privatekey.js b/lib/privatekey.js
index c0569fe..794860c 100644
--- a/lib/privatekey.js
+++ b/lib/privatekey.js
@@ -97,7 +97,7 @@ PrivateKey.prototype._classifyArguments = function(data, network) {
   };
 
   // detect type of data
-  if (_.isUndefined(data)){
+  if (_.isUndefined(data) || _.isNull(data)){
     info.bn = PrivateKey._getRandomBN();
   } else if (data instanceof BN) {
     info.bn = data;
@@ -105,6 +105,9 @@ PrivateKey.prototype._classifyArguments = function(data, network) {
     info = PrivateKey._transformBuffer(data, network);
   } else if (PrivateKey._isJSON(data)){
     info = PrivateKey._transformJSON(data);
+  } else if (!network && Networks.get(data)) {
+    info.bn = PrivateKey._getRandomBN();
+    info.network = Networks.get(data);
   } else if (typeof(data) === 'string'){
     if (JSUtil.isHexa(data)) {
       info.bn = BN(new Buffer(data, 'hex'));
diff --git a/test/privatekey.js b/test/privatekey.js
index 6ecda31..7cae44b 100644
--- a/test/privatekey.js
+++ b/test/privatekey.js
@@ -31,6 +31,18 @@ describe('PrivateKey', function() {
     should.exist(b.bn);
   });
 
+  it('should create a new random testnet private key with only one argument', function() {
+    var a = new PrivateKey(Networks.testnet);
+    should.exist(a);
+    should.exist(a.bn);
+  });
+
+  it('should create a new random testnet private key with empty data', function() {
+    var a = new PrivateKey(null, Networks.testnet);
+    should.exist(a);
+    should.exist(a.bn);
+  });
+
   it('should create a private key from WIF string', function() {
     var a = new PrivateKey('L3T1s1TYP9oyhHpXgkyLoJFGniEgkv2Jhi138d7R2yJ9F4QdDU2m');
     should.exist(a);