Citadel Investment Group’s flagship fund is down by double-digits after the worst month in its history.

The $18 billion fund lost 15% in September, in part due to new restrictions on short-selling and lack of available money to borrow, the Financial Times reports. Prior to last month, the fund’s worst month was 14 years ago, when it sank 4%. The fund is down 18% year-to-date.

Citadel is more used to profiting from the market turmoil than suffering through it. The Chicago hedge fund giant has made a cottage industry of buying the portfolios of collapsing hedge funds, such as Amaranth Advisors and Sowood Capital Management.