1 files changed, 4 insertions, 2 deletions
diff --git a/lib/contract.js b/lib/contract.js
index 4cb202255..eb7fbf018 100644
--- a/lib/contract.js
+++ b/lib/contract.js
@@ -57,8 +57,10 @@ var contract = function (address, desc) {
                 transact: function (extra) {
                     extra = extra || {};
                     extra.to = address;
-                    extra.data = parsed;
-                    return web3.eth.transact(extra).then(onSuccess);
+                    return abi.methodSignature(desc, method.name).then(function (signature) {
+                        extra.data = signature.slice(0, 2 + ETH_METHOD_SIGNATURE_LENGTH * 2) + parsed;
+                        return web3.eth.transact(extra).then(onSuccess);
+                    });
                 }
             };
         };