Ford is recalling nearly 2 million of its popular F-150 pickups because of a seatbelt problem that could result in smoke, and possibly even a fire, inside the vehicle.

The F-150 is part of Ford’s broader F-Series line-up of full-size trucks that collectively make up the best-selling vehicle in the U.S., with demand growing sharply over the last several years.

The problem involves a device known as a pretensioner, which uses a small, pyrotechnic charge, much like those found in airbags. But, in this case, they are designed to cinch a passenger’s seatbelt tight when a crash is detected to reduce the risk of injury or death.

Unfortunately, according to Ford, the seatbelt pretensioner system used on some F-150 models “can generate excessive sparks when they deploy.”

Complicating matters, gases created by the pretensioner “may ignite,” Ford said in a statement, adding that “if this gas ignites, components behind the B-pillar, such as insulation and carpet may subsequently catch fire.”

The B-pillar is the post that separates a vehicle’s front and rear doors.