Traders have boosted their Japanese bond futures holdings to the most in more than 23 years, an indication they are ratcheting bets that the central bank will make further adjustments.

Open interest in JGB futures, which may be used to take short positions, rose to 183,960 contracts on Monday, the most since April 2000, according to data compiled by Bloomberg. The surge suggests that traders are betting against Japanese bonds after the Bank of Japan last week surprised markets by widening the allowable trading band in the 10-year yield to 1%.

Investors may be anticipating more changes by the BOJ by conducting a trade that’s been called the widow maker, as the central bank intervening in markets to anchor the yield curve ended up saddling investors with crippling losses. Even though the trading band was widened, it’s still a risky gamble after the BOJ again dipped into the market Monday when the yield on 10-year notes rose to their highest in nine years.

Traders and investors should challenge the BOJ ahead of a policy meeting, not now, as there’s a chance shorts could get burned again, said Shoki Omori, chief desk strategist at Mizuho Securities Co. in Tokyo. Bets may be pared for a short period before rising ahead of September’s meeting, he said.

Read More: BOJ Watchers See No Further Policy Shift in 2023 After YCC Tweak

Still, the widow-maker bet has paid off for some funds including RBC BlueBay Asset Management. The yield on the 10-year note has climbed about 18 basis points this year, and many Tokyo-based economists expect it to settle around 0.7% to 0.8% by year-end. The bond traded at 0.595% on Tuesday.

--With assistance from Mark Cranfield.