While the billionaire didn’t say when a market turn might come, or what the magnitude of the fall might be, he did pinpoint a likely culprit.

Just as portfolio insurance caused the 1987 rout, he says, the new danger zone is the half-trillion dollars in risk parity funds. These funds aim to systematically spread risk equally across different asset classes by putting more money in lower volatility securities and less in those whose prices move more dramatically.

Because risk-parity funds have been scooping up equities of late as volatility hit historic lows, some market participants, Jones included, believe they’ll be forced to dump them quickly in a stock tumble, exacerbating any decline.

“Risk parity,” Jones told the Goldman audience, “will be the hammer on the downside.”