```\nfunction _withdrawERC20(address account, ERC20 token)\n  internal\n  returns (uint256 withdrawn)\n{\n  // leave balance of 1 for gas efficiency\n  // underflow if erc20Balance is 0\n  withdrawn = erc20Balances[token][account] - 1;\n  erc20Balances[token][account] = 1;\n  token.safeTransfer(account, withdrawn);\n}\n```\n