Traders looking to bet against the beleaguered United States Oil Fund LP are going to have a harder time of it today.

The $3 billion exchange-traded fund’s staggering 25% plunge Tuesday triggered the U.S. Securities and Exchange Commission’s “alternative uptick rule,” which restricts short selling on a stock that has dropped more than 10% from the previous day’s close. After that point, short sale orders can only happen when the stock is ticking higher, on the so-called “offer” side of the spread, in trader parlance.

The ETF, which trades under the ticker USO, has plummeted more than 39% this week as crude oil prices swoon amid a supply glut. It first triggered the SEC’s circuit breaker on Monday, falling as much as 12%. USO has taken a series of actions to shore up its share price, including switching its holdings to longer-dated futures contracts on Tuesday and announcing a one-for-eight reverse share split on Wednesday.

“It will somewhat protect some of these unknowing retail investors who bought in at premium,” said Eric Balchunas, senior ETF analyst at Bloomberg Intelligence. “Hedge funds were probably looking to sell at the premium and then buy back when creations opened back up.”

USO dropped more than 10% Wednesday to a record low. The declines came even as crude oil rebounded to above $13 a barrel after President Donald Trump ordered the Navy to destroy any Iranian gun boats that harass American ships at sea.

This article was provided by Bloomberg News.