Billionaire investor George Soros, who rose to fame and fortune by betting against the sterling in 1992, on Monday showed his latest hand: nearly doubling down on his bearish bet against the market.

The 86-year-old's fund disclosed in a regulatory filing it had increased its bet against the S&P 500, the main index used to measure big-stock performance in the US, reporting "put" options on roughly 4 million shares as of June 30 in an exchange-traded fund that tracks the index. That's up from "puts" on 2.1 million shares as of March 31.