Goldman Sachs Group Inc. and JPMorgan Chase & Co. have been advising investors to use call options to position for a U.S. equity rebound from this month’s sell-off. It looks like someone got the message.

The biggest trade among U.S.-listed contracts Wednesday was a call spread where one investor appears to have bought $315 October calls and sold the $320 October calls on the SPDR S&P 500 ETF. The transaction amounted to the equivalent of 11 million shares and positions for the ETF to rally about 10%. It was funded in part by selling the $270-$276 put spread on the equivalent of 1.1 million shares. The $315 calls, if fully exercised could yield a net position of about $3.5 billion for the investor.

“While the call spread on the surface looks bullish, being short the downside put spread makes this a very risky trade,” Alon Rosin, Oppenheimer’s head of institutional equity derivatives said in an interview Wednesday. The strategy could also potentially be a hedge against a large portfolio of shorts and help offset a quick market surge, he said.

The big options bet came amid a drop of as much as 3% in the S&P 500 as mounting signs of a global economic slowdown prompted a sell-off of riskier assets and drove demand for sovereign bonds. The benchmark for U.S. equities has fallen more than 6% from its July 26 record, with most of this month’s slide attributable to the latest escalation in the U.S.-China trade war.

Last week, JPMorgan told clients to use index options to position for a recovery in the S&P 500, citing the bank’s 3,200 year-end price target. On Monday, strategists at Goldman made a similar recommendation, saying that relatively low implied volatility has made prices attractive.