Amazon has paused testing of its delivery drones following a crash involving two of its models, according to Bloomberg. It’s the latest setback for Amazon’s beleaguered Prime Air program, which aims to deliver around 500 million packages a year to customers by the end of the decade.

Amazon has stopped its drone delivery operations in the U.S. following a crash during testing. The incident, which took place in Pendleton, Oregon, in December, involved two drones colliding during rainy weather.

Amazon is halting all commercial drone deliveries after two of its latest drone models crashed in rainy weather at a testing facility,