diff --git a/contracts/handlers/DepositDataHelper.sol b/contracts/handlers/DepositDataHelper.sol
index a157646c..5f84ad28 100644
--- a/contracts/handlers/DepositDataHelper.sol
+++ b/contracts/handlers/DepositDataHelper.sol
@@ -10,6 +10,8 @@ import "../interfaces/ISygmaMessageReceiver.sol";
     @author ChainSafe Systems.
  */
 contract DepositDataHelper is ERCHandlerHelpers {
+    using SanityChecks for *;
+
     address public immutable _defaultMessageReceiver;
     uint16 internal constant maxReturnBytes = 256;
     address internal constant transformRecipient = address(0);
@@ -54,13 +56,14 @@ contract DepositDataHelper is ERCHandlerHelpers {
         uint256 lenDestinationRecipientAddress;
 
         (amount, lenDestinationRecipientAddress) = abi.decode(data, (uint256, uint256));
-        address recipientAddress = address(bytes20(bytes(data[64:64 + lenDestinationRecipientAddress])));
+        lenDestinationRecipientAddress.mustBe(20);
+        address recipientAddress = address(bytes20(bytes(data[64:84])));
 
         address tokenAddress = _resourceIDToTokenContractAddress[resourceID];
         uint256 externalAmount = convertToExternalBalance(tokenAddress, amount);
 
         // Optional message recipient transformation.
-        uint256 pointer = 64 + lenDestinationRecipientAddress;
+        uint256 pointer = 84;
         uint256 gas;
         uint256 messageLength;
         bytes memory message;
diff --git a/contracts/handlers/ERC1155Handler.sol b/contracts/handlers/ERC1155Handler.sol
index a2d894b1..b11a531f 100644
--- a/contracts/handlers/ERC1155Handler.sol
+++ b/contracts/handlers/ERC1155Handler.sol
@@ -71,6 +71,7 @@ contract ERC1155Handler is IHandler, ERCHandlerHelpers, ERC1155Safe, ERC1155Hold
 
         (tokenIDs, amounts, recipient, transferData) = abi.decode(data, (uint[], uint[], bytes, bytes));
 
+        recipient.length.mustBe(20);
         bytes20 recipientAddress;
 
         assembly {
diff --git a/contracts/handlers/ERC721Handler.sol b/contracts/handlers/ERC721Handler.sol
index 6f8fa9b0..c5fcaa72 100644
--- a/contracts/handlers/ERC721Handler.sol
+++ b/contracts/handlers/ERC721Handler.sol
@@ -92,7 +92,8 @@ contract ERC721Handler is IHandler, ERCHandlerHelpers, ERC721Safe {
         bytes memory metaData;
 
         (tokenID, lenDestinationRecipientAddress) = abi.decode(data, (uint, uint));
-        offsetMetaData = 64 + lenDestinationRecipientAddress;
+        lenDestinationRecipientAddress.mustBe(20);
+        offsetMetaData = 84;
         destinationRecipientAddress = bytes(data[64:offsetMetaData]);
         lenMetaData = abi.decode(data[offsetMetaData:], (uint));
         metaData = bytes(data[offsetMetaData + 32:offsetMetaData + 32 + lenMetaData]);
diff --git a/contracts/handlers/GmpHandler.sol b/contracts/handlers/GmpHandler.sol
index 229acce1..2a63bbc1 100644
--- a/contracts/handlers/GmpHandler.sol
+++ b/contracts/handlers/GmpHandler.sol
@@ -3,6 +3,7 @@
 pragma solidity 0.8.11;
 
 import "../interfaces/IHandler.sol";
+import "../utils/SanityChecks.sol";
 
 /**
     @title Handles generic deposits and deposit executions.
@@ -10,6 +11,8 @@ import "../interfaces/IHandler.sol";
     @notice This contract is intended to be used with the Bridge contract.
  */
 contract GmpHandler is IHandler {
+    using SanityChecks for *;
+
     uint256 public constant MAX_FEE = 1000000;
 
     address public immutable _bridgeAddress;
@@ -165,10 +168,13 @@ contract GmpHandler is IHandler {
 
         maxFee                            = uint256(bytes32(data[:pointer += 32])); 
         lenExecuteFuncSignature           = uint16(bytes2(data[pointer:pointer += 2]));
+        lenExecuteFuncSignature.mustBe(4);
         executeFuncSignature              = bytes4(data[pointer:pointer += lenExecuteFuncSignature]);
         lenExecuteContractAddress         = uint8(bytes1(data[pointer:pointer += 1]));
+        lenExecuteContractAddress.mustBe(20);
         executeContractAddress            = address(uint160(bytes20(data[pointer:pointer += lenExecuteContractAddress])));
         lenExecutionDataDepositor         = uint8(bytes1(data[pointer:pointer += 1]));
+        lenExecutionDataDepositor.mustBe(20);
         executionDataDepositor            = address(uint160(bytes20(data[pointer:pointer += lenExecutionDataDepositor])));
         executionData                     = bytes(data[pointer:]);
 
diff --git a/contracts/handlers/XC20Handler.sol b/contracts/handlers/XC20Handler.sol
index 3c9b01ec..a6e9c393 100644
--- a/contracts/handlers/XC20Handler.sol
+++ b/contracts/handlers/XC20Handler.sol
@@ -72,7 +72,8 @@ contract XC20Handler is IHandler, ERCHandlerHelpers, XC20Safe {
         bytes  memory destinationRecipientAddress;
 
         (amount, lenDestinationRecipientAddress) = abi.decode(data, (uint, uint));
-        destinationRecipientAddress = bytes(data[64:64 + lenDestinationRecipientAddress]);
+        lenDestinationRecipientAddress.mustBe(20);
+        destinationRecipientAddress = bytes(data[64:84]);
 
         bytes20 recipientAddress;
         address tokenAddress = _resourceIDToTokenContractAddress[resourceID];
diff --git a/contracts/utils/SanityChecks.sol b/contracts/utils/SanityChecks.sol
index 976f7ee7..50a9fb64 100644
--- a/contracts/utils/SanityChecks.sol
+++ b/contracts/utils/SanityChecks.sol
@@ -8,9 +8,15 @@ pragma solidity 0.8.11;
  */
 library SanityChecks {
     error ZeroAddress();
+    error UnexpectedValue(uint256 actual, uint256 expected);
 
     function mustNotBeZero(address addr) internal pure returns(address) {
         if (addr == address(0)) revert ZeroAddress();
         return addr;
     }
+
+    function mustBe(uint256 actual, uint256 expected) internal pure returns(uint256) {
+        if (actual != expected) revert UnexpectedValue(actual, expected);
+        return actual;
+    }
 }