The global housing market could be a bubble in danger of a correction, and U.S. home prices alone could drop by 19.5%, economists at the Dallas Federal Reserve warn.

Citing an affordability crisis, authors Lauren Black and Enrique Martinez-Garcia wrote in a Tuesday Dallas Fed report: “If the observed price-to-rent ratio grows at an explosive rate relative to its fundamental-based ratio estimated with long-term interest rate and rent growth data, the bubble hypothesis merits attention,” Business Insider reports.

The U.S. and German housing markets, in particular, face erratic real estate market activity and rising interest rates, and with that, rising mortgage rates, that are driving a “risk of a deep global housing slide,” the economists warned.

The housing market faces more risk if the Federal Reserve decides to become more restrictive with its monetary policy, they said.

If U.S. home prices fell, or corrected, by 19.5%, the real estate market would be more in line “with its fundamentals” and become more affordable, the researchers said.

Thirty-year mortgages topped 7% in October and are currently 6.62%. Case-Shiller data Tuesday shows that U.S. home prices have fallen for six months straight. Existing-home sales have declined for six straight months, according to the National Association of Realtors.

Home prices are now 4.1% below their June peak, and Goldman Sachs forecasts home prices will decline another 6.1% in 2023.