diff --git a/lib/bitauth-browserify.js b/lib/bitauth-browserify.js
index 956524a..4895a02 100644
--- a/lib/bitauth-browserify.js
+++ b/lib/bitauth-browserify.js
@@ -36,7 +36,8 @@ BitAuth._getPublicKeyFromPrivateKey = function(privkey) {
 };
 
 BitAuth._sign = function(hashBuffer, privkey) {
-  var signature = ecdsa.sign(hashBuffer.toString('hex'), privkey);
+  var keys = ecdsa.keyFromPrivate(privkey, 'hex');
+  var signature = keys.sign(hashBuffer.toString('hex'));
   var hexsignature = signature.toDER('hex');
   return hexsignature;
 };