Stock-related derivatives positions caused losses for Goldman Sachs in the second quarter, and some investors worry they may create trouble for Warren Buffett’s Berkshire Hathaway too.

As for Goldman, it took a loss through derivatives it sold to clients to protect them against volatility in the stock market. That meant Goldman itself was betting against higher volatility, which surged in May.

“Primarily in response to our client needs, our equity derivatives business was short volatility entering the second quarter and posted poor results,” Goldman CFO David Viniar said in a press conference, Bloomberg reports.

“We had that position going into the quarter, and volatility just spiked.”

Berkshire has sold puts on stock indexes, a bullish bet on stocks. The company has about $37 billion at risk in its equity-linked contracts, Bloomberg reports.

“He (Buffett) handcuffed himself during the crisis by selling puts at the top of the market,” said Jeff Matthews, founder of hedge fund Ram Partners, told Bloomberg

“His whole company is a bet on a rising market over a very long period of time. So to then sell derivatives on the basis of that is doubling the chips on black.”

Derivatives trading has become a key source of profit for Wall Street firms like Goldman.

Brad Hintz, an analyst at Sanford Bernstein, estimates that derivatives account for about 15 percent of banks’ bond trading and 20 percent of their stock trading, according to the Financial Times.