diff --git a/contracts/Feeless.sol b/contracts/Feeless.sol
index ed0b758..c34ff71 100644
--- a/contracts/Feeless.sol
+++ b/contracts/Feeless.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.23;
+pragma solidity ^0.4.24;
 
 import { ECRecovery } from "zeppelin-solidity/contracts/ECRecovery.sol";
 
@@ -22,7 +22,8 @@ contract Feeless {
         require(this == target);
         
         bytes memory prefix = "\x19Ethereum Signed Message:\n32";
-        bytes32 hash = keccak256(prefix, keccak256(target, data, nonce));
+        bytes32 payload = keccak256(abi.encodePacked(target, data, nonce));
+        bytes32 hash = keccak256(abi.encodePacked(prefix, payload));
         msgSender = ECRecovery.recover(hash, sig);
         require(msgSender == sender);
         require(nonces[msgSender]++ == nonce);
diff --git a/contracts/Migrations.sol b/contracts/Migrations.sol
index a1151cd..c94abbf 100644
--- a/contracts/Migrations.sol
+++ b/contracts/Migrations.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.4.23;
+pragma solidity ^0.4.24;
 
 
 contract Migrations {
@@ -10,7 +10,7 @@ contract Migrations {
         if (msg.sender == owner) _;
     }
 
-    function Migrations() public {
+    constructor () public {
         owner = msg.sender;
     }