One of the year’s top-performing hedge funds’ luck ran out last month.

Clarium Capital Management, the $7 billion San Francisco hedge fund set up by PayPal founder Peter Thiel, posted its biggest-ever monthly loss in August. The firm’s eponymous flagship lost about 13%, Bloomberg News reports, cutting it’s year-to-date return to 27.6%.

Clarium was burned by the dollar’s rally against European currencies. The hedge fund bet that the dollar’s recent doldrums would continue, only to see the U.S. currency post its biggest rise against the euro in eight years.

Prior to last month, Clarium’s worst month was March 2004, when it lost 11.4%.