Boeing's first Starliner flight with astronauts on board was called off in the final minutes on Saturday.

The company was targeting a launch on June 1 at 12:25 p.m. ET of its capsule, which is carrying astronauts to the International Space Station for the first time in a final major test of the system.

The launch’s hold was automatically issued for an unspecified reason, NASA said on its broadcast, with under four minutes remaining in the countdown. Holds in a rocket launch countdown are a fairly common occurrence. The crew on board are safe and will disembark shortly.

Two NASA astronauts are aboard the Starliner capsule, which would be carried by United Launch Alliance’s Atlas V rocket to the International Space Station.

Boeing already has backup launch dates scheduled, including Sunday at 12:03 p.m. EDT. Depending on the cause of the launch scrub, Boeing and NASA can reschedule the launch for another attempt 24 hours later, or target alternative launch dates of June 5th or June 6th.