_Follow along with this video:_ --- ### Mitigation Integer over/underflow is actually fairly straightforward to mitigate against. ```js function selectWinner() external { require(block.timestamp >= raffleStartTime + raffleDuration, "PuppyRaffle: Raffle not over"); require(players.length >= 4, "PuppyRaffle: Need at least 4 players"); uint256 winnerIndex = uint256(keccak256(abi.encodePacked(msg.sender, block.timestamp, block.difficulty))) % players.length; address winner = players[winnerIndex]; uint256 totalAmountCollected = players.length * entranceFee; uint256 prizePool = (totalAmountCollected * 80) / 100; uint256 fee = (totalAmountCollected * 20) / 100; // @Audit: Newer version of Solidity, Bigger Uints totalFees = totalFees + uint64(fee); ``` In our `Puppy Raffle` protocol we would likely suggest a newer Solidity version. The use of a `uint64` is also just silly. Foundry allows us to verify the max sizes of the numbers really conveniently through a `chisel` command. Typing `chisel` will start `chisel`, the command `type(uint64).max` will give an output like this: ```bash Welcome to Chisel! Type `!help` to show available commands. ➜ type(uint64).max Type: uint ├ Hex: 0x000000000000000000000000000000000000000000000000ffffffffffffffff └ Decimal: 18446744073709551615 ➜ ``` _18 ETH due to having 18 decimal places_ If `Puppy Raffle` receives more than 18 ETH in fees, we're going to see overflow issues! Experiment with `chisel` and try different `uint/int` types to get a sense for how big/small some of these common numbers are!