diff --git a/contracts/ERC20Mixer.sol b/contracts/ERC20Mixer.sol
index aeb1ac9..8a815c5 100644
--- a/contracts/ERC20Mixer.sol
+++ b/contracts/ERC20Mixer.sol
@@ -56,6 +56,8 @@ contract ERC20Mixer is Mixer {
         )
     );
     require(success, "not enough allowed tokens");
+
+    // if contract returns some data let's make sure that is `true` according to standard
     if (data.length > 0) {
       assembly {
         success := mload(add(data, 0x20))
@@ -75,6 +77,8 @@ contract ERC20Mixer is Mixer {
         )
     );
     require(success, "not enough tokens");
+
+    // if contract returns some data let's make sure that is `true` according to standard
     if (data.length > 0) {
       assembly {
         success := mload(add(data, 0x20))
diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 7cae6f2..262967c 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -29,7 +29,7 @@ contract Mixer is MerkleTreeWithHistory {
   uint256 public mixDenomination;
 
   event Deposit(uint256 indexed commitment, uint256 leafIndex, uint256 timestamp);
-  event Withdraw(address to, uint256 nullifierHash, address relayer, uint256 fee);
+  event Withdraw(address to, uint256 nullifierHash, address indexed relayer, uint256 fee);
 
   /**
     @dev The constructor
diff --git a/test/ERC20Mixer.test.js b/test/ERC20Mixer.test.js
index e9f72c2..8c69835 100644
--- a/test/ERC20Mixer.test.js
+++ b/test/ERC20Mixer.test.js
@@ -127,7 +127,7 @@ contract('ERC20Mixer', accounts => {
         // public
         root,
         nullifierHash: pedersenHash(deposit.nullifier.leInt2Buff(31)),
-        relayer: operator,
+        relayer,
         receiver,
         fee,
 
@@ -160,15 +160,15 @@ contract('ERC20Mixer', accounts => {
       const balanceRecieverAfter = await token.balanceOf(toHex(receiver.toString()))
       const ethBalanceRecieverAfter = await web3.eth.getBalance(toHex(receiver.toString()))
       const feeBN = toBN(fee.toString())
-      balanceMixerAfter.should.be.eq.BN(toBN(balanceMixerBefore).sub(toBN(value)))
-      balanceRelayerAfter.should.be.eq.BN(toBN(balanceRelayerBefore))
+      balanceMixerAfter.should.be.eq.BN(toBN(balanceMixerBefore).sub(toBN(tokenDenomination)))
+      balanceRelayerAfter.should.be.eq.BN(toBN(balanceRelayerBefore).add(feeBN))
       ethBalanceOperatorAfter.should.be.eq.BN(toBN(ethBalanceOperatorBefore))
       balanceRecieverAfter.should.be.eq.BN(toBN(balanceRecieverBefore).add(toBN(tokenDenomination).sub(feeBN)))
       ethBalanceRecieverAfter.should.be.eq.BN(toBN(ethBalanceRecieverBefore).add(toBN(value)))
 
       logs[0].event.should.be.equal('Withdraw')
       logs[0].args.nullifierHash.should.be.eq.BN(toBN(input.nullifierHash.toString()))
-      logs[0].args.relayer.should.be.eq.BN(operator)
+      logs[0].args.relayer.should.be.eq.BN(relayer)
       logs[0].args.fee.should.be.eq.BN(feeBN)
       isSpent = await mixer.isSpent(input.nullifierHash.toString(16).padStart(66, '0x00000'))
       isSpent.should.be.equal(true)
diff --git a/test/MerkleTreeWithHistory.test.js b/test/MerkleTreeWithHistory.test.js
index f6f5396..742c00c 100644
--- a/test/MerkleTreeWithHistory.test.js
+++ b/test/MerkleTreeWithHistory.test.js
@@ -190,6 +190,15 @@ contract('MerkleTreeWithHistory', accounts => {
       error = await merkleTreeWithHistory.insert(1).should.be.rejected
       error.reason.should.be.equal('Merkle tree is full')
     })
+
+    it.skip('mimc gas', async () => {
+      levels = 6
+      zeroValue = 1337
+      merkleTreeWithHistory = await MerkleTreeWithHistory.new(levels, zeroValue)
+
+      const gas = await merkleTreeWithHistory.hashLeftRight.estimateGas(zeroValue, zeroValue)
+      console.log('gas', gas - 21000)
+    })
   })
 
   afterEach(async () => {