diff --git a/cli.js b/cli.js
index 88f6978..61aae9a 100755
--- a/cli.js
+++ b/cli.js
@@ -150,13 +150,13 @@ async function withdraw(note, receiver) {
   console.log('Getting current state from mixer contract')
   const events = await mixer.getPastEvents('Deposit', { fromBlock: mixer.deployedBlock, toBlock: 'latest' })
   const leaves = events
-    .sort((a, b) => a.returnValues.leafIndex.sub(b.returnValues.leafIndex)) // Sort events in chronological order
+    .sort((a, b) => a.returnValues.leafIndex - b.returnValues.leafIndex) // Sort events in chronological order
     .map(e => e.returnValues.commitment)
   const tree = new merkleTree(MERKLE_TREE_HEIGHT, leaves)
 
   // Find current commitment in the tree
   let depositEvent = events.find(e => e.returnValues.commitment.eq(paddedCommitment))
-  let leafIndex = depositEvent ? depositEvent.returnValues.leafIndex.toNumber() : -1
+  let leafIndex = depositEvent ? depositEvent.returnValues.leafIndex : -1
 
   // Validate that our data is correct
   const isValidRoot = await mixer.methods.isKnownRoot(await tree.root()).call()
diff --git a/contracts/ERC20Mixer.sol b/contracts/ERC20Mixer.sol
index 8c44ac7..4d07fd8 100644
--- a/contracts/ERC20Mixer.sol
+++ b/contracts/ERC20Mixer.sol
@@ -19,7 +19,7 @@ contract ERC20Mixer is Mixer {
   constructor(
     IVerifier _verifier,
     uint256 _denomination,
-    uint8 _merkleTreeHeight,
+    uint32 _merkleTreeHeight,
     address _operator,
     address _token
   ) Mixer(_verifier, _denomination, _merkleTreeHeight, _operator) public {
diff --git a/contracts/ETHMixer.sol b/contracts/ETHMixer.sol
index 90984c7..b88a734 100644
--- a/contracts/ETHMixer.sol
+++ b/contracts/ETHMixer.sol
@@ -17,7 +17,7 @@ contract ETHMixer is Mixer {
   constructor(
     IVerifier _verifier,
     uint256 _denomination,
-    uint8 _merkleTreeHeight,
+    uint32 _merkleTreeHeight,
     address _operator
   ) Mixer(_verifier, _denomination, _merkleTreeHeight, _operator) public {
   }
diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index 6c3b1d7..36161a4 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -19,26 +19,27 @@ contract MerkleTreeWithHistory {
   uint256 public constant FIELD_SIZE = 21888242871839275222246405745257275088548364400416034343698204186575808495617;
   uint256 public constant ZERO_VALUE = 5702960885942360421128284892092891246826997279710054143430547229469817701242; // = MiMC("tornado")
 
-  uint256 public levels;
+  uint32 public levels;
 
   // the following variables are made public for easier testing and debugging and
   // are not supposed to be accessed in regular code
-  uint256 public constant ROOT_HISTORY_SIZE = 100;
+  uint32 public constant ROOT_HISTORY_SIZE = 100;
   uint256[ROOT_HISTORY_SIZE] public roots;
-  uint256 public currentRootIndex = 0;
+  uint32 public currentRootIndex = 0;
   uint32 public nextIndex = 0;
   uint256[] public filledSubtrees;
   uint256[] public zeros;
 
-  constructor(uint256 _treeLevels) public {
+  constructor(uint32 _treeLevels) public {
     require(_treeLevels > 0, "_treeLevels should be greater than zero");
+    require(_treeLevels < 32, "_treeLevels should be less than 32");
     levels = _treeLevels;
 
     uint256 currentZero = ZERO_VALUE;
     zeros.push(currentZero);
     filledSubtrees.push(currentZero);
 
-    for (uint8 i = 1; i < levels; i++) {
+    for (uint32 i = 1; i < levels; i++) {
       currentZero = hashLeftRight(currentZero, currentZero);
       zeros.push(currentZero);
       filledSubtrees.push(currentZero);
@@ -61,15 +62,15 @@ contract MerkleTreeWithHistory {
     return R;
   }
 
-  function _insert(uint256 _leaf) internal returns(uint256 index) {
+  function _insert(uint256 _leaf) internal returns(uint32 index) {
     uint32 currentIndex = nextIndex;
-    require(currentIndex != 2**levels, "Merkle tree is full. No more leafs can be added");
+    require(currentIndex != uint32(2)**levels, "Merkle tree is full. No more leafs can be added");
     nextIndex += 1;
     uint256 currentLevelHash = _leaf;
     uint256 left;
     uint256 right;
 
-    for (uint256 i = 0; i < levels; i++) {
+    for (uint32 i = 0; i < levels; i++) {
       if (currentIndex % 2 == 0) {
         left = currentLevelHash;
         right = zeros[i];
@@ -97,7 +98,7 @@ contract MerkleTreeWithHistory {
     if (_root == 0) {
       return false;
     }
-    uint256 i = currentRootIndex;
+    uint32 i = currentRootIndex;
     do {
        if (_root == roots[i]) {
            return true;
diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 7c703be..4fa301f 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -35,7 +35,7 @@ contract Mixer is MerkleTreeWithHistory {
     _;
   }
 
-  event Deposit(uint256 indexed commitment, uint256 leafIndex, uint256 timestamp);
+  event Deposit(uint256 indexed commitment, uint32 leafIndex, uint256 timestamp);
   event Withdrawal(address to, uint256 nullifierHash, address indexed relayer, uint256 fee);
 
   /**
@@ -48,7 +48,7 @@ contract Mixer is MerkleTreeWithHistory {
   constructor(
     IVerifier _verifier,
     uint256 _denomination,
-    uint8 _merkleTreeHeight,
+    uint32 _merkleTreeHeight,
     address _operator
   ) MerkleTreeWithHistory(_merkleTreeHeight) public {
     require(_denomination > 0, "denomination should be greater than 0");
@@ -64,7 +64,7 @@ contract Mixer is MerkleTreeWithHistory {
   function deposit(uint256 _commitment) public payable {
     require(!isDepositsDisabled, "deposits are disabled");
     require(!commitments[_commitment], "The commitment has been submitted");
-    uint256 insertedIndex = _insert(_commitment);
+    uint32 insertedIndex = _insert(_commitment);
     commitments[_commitment] = true;
     _processDeposit();