Hedge fund guru David Einhorn says he increased his bullish bets last month, but remains concerned about several issues, including the Federal Reserve’s low-interest rate policy.

In a conference call with Greenlight Capital Re investors, Einhorn said that he increased his bullish positions thanks to better-than-expected corporate earnings results, Bloomberg reports. But, he added, “This enthusiasm is tempered by our continued concern about the structural sovereign-debt problems in Europe and Japan, a slowing Chinese economy, and high oil prices and general inflation connected to the Fed’s continued insistence on maintaining an emergency zero percent interest-rate policy, which we believe is no longer useful or effective.”

Greenlight Re’s investment portfolio’s net-long position rose to 39% in April from 32% at the end of March, Einhorn said. He said he also added short bets in the first three months of the year as the market rallied, according to Bloomberg.