Japanese retail investors are returning to a trade that has burned them repeatedly in the past: buying the Turkish lira.

The currency, which has plunged more than 16% against the yen this year, has become one of the hottest bets for Japan’s risk-hungry day traders. They held almost 900,000 margin contracts that track the pair as of Nov. 12, according to data from Tokyo Financial Exchange — near an all-time high.

That is raising fears about a painful blowup for investors whose unraveling bets could quickly spill over to other markets.