A pair of U.S. astronauts who test-piloted a new Boeing spaceship in June may not fly home on the craft they rode in on.

While Boeing has conducted a variety of tests in space and on the ground to try to better understand problems with its Starliner capsule, now docked at the International Space Station, NASA apparently has been busy making contingency plans for an alternative way to bring Commander Barry “Butch” Wilmore, 61, and Sunita “Suni” Williams, 58, back to Earth.

NASA officials said they would decide whether the two would return on Starliner or Boeing’s competitor, SpaceX‘s Dragon capsule, by mid-August. That possible shift in plans, announced during a call with reporters on Wednesday, comes after two months of the agency insisting it wasn’t entertaining the idea of changing horses — or, rather, spacecraft — in midstream.

If NASA chooses to use SpaceX for Wilmore and Williams’ return voyage, they would remain at the space station for at least another six or seven months. That would extend their originally planned eight-day visit to a nine-month layover and would have a cascading effect on the crew lineups for future expeditions.