Ford is testing a converted F-150 pickup truck that is likely a prototype of its upcoming Bronco SUV.

A potential switch to the full-size truck frame for the highly-anticipated Bronco is big news. Spy photographers spotted the strange vehicle on public roads near the company’s headquarters in Dearborn, Mich., this week.

The vehicle resembles a single-cab Ford F-150 with the front fascia and off-road tires of the extreme F-150 Raptor. However, sales of single cab full-size trucks are rare. This is likely a disguised version of the Bronco SUV expected in 2020.

Previous Bronco test mules used the smaller frame of the Ford Ranger midsize truck. That Bronco prototype had compact dimensions and 33-inch tires suited for rugged adventure.

The new Bronco test vehicle is even more well-equipped. It has visibly stronger components, 35-inch tires and a large rear axle housing. The rear shocks are the Fox units equipped on 2017-18 F-150 Raptors.

Because of the size of the F-150-based Bronco, Trucks.com believes this vehicle is the true Bronco SUV. The previous Ranger-based vehicle is likely a smaller “Baby Bronco” version. Analysts expected the compact Bronco to use a crossover-like unibody frame. But the spy photos make it appear that both Bronco models will be truck-based.

The single-cab configuration of the spied vehicle could also foreshadow a two-door version of the SUV. But, few two-door SUVs are available in the U.S. market. Only the Jeep Wrangler and future Land Rover Defender 90 fit the configuration.

Instead, Ford could have shortened the F-150 – the bed also appears to be chopped – in order to mimic the exterior dimensions of its Bronco midsize SUV.

The Ford Bronco will enter production in 2020.