Warren Buffett is lobbying the U.S. Senate to avoid derivatives reforms that would require, among other things, financial institutions to put up collateral to cover potential losses.

According to the WSJ, Buffett, who has referred to derivatives as “financial weapons of mass destruction,” is leaning on Nebraska Senator Ben Nelson to help him with an exemption that would potentially help Berkshire Hathaway’s (BRKa) (BRKb) $63 billion derivatives portfolio avoid a financial hit.