diff --git a/packages/protocol/contracts/common/Accounts.sol b/packages/protocol/contracts/common/Accounts.sol
index 462e7a499a6..b24cc6c8b2a 100644
--- a/packages/protocol/contracts/common/Accounts.sol
+++ b/packages/protocol/contracts/common/Accounts.sol
@@ -298,7 +298,7 @@ contract Accounts is
     uint256 numberRoots = offchainStorageRoots[account].length;
     uint256 totalLength = 0;
     for (uint256 i = 0; i < numberRoots; i++) {
-      totalLength += offchainStorageRoots[account][i].length;
+      totalLength = totalLength.add(offchainStorageRoots[account][i].length);
     }
 
     bytes memory concatenated = new bytes(totalLength);