The United States Federal Aviation Administration, which has been investigating Boeing’s grounded 737 Max in the wake of two crashes caused by malfunctions of its onboard systems, has discovered another, unrelated safety flaw. Reuters was first to report the news, with its sources indicating that the new safety issue was discovered in simulator tests last week, and now Boeing faces increased delays — which may include the potential need for hardware fixes — before it’s able to regain certification for airworthiness of its 737 Max.

A subsequent emailed statement from the US regulator has confirmed, without elaborating, that “The FAA recently found a potential risk that Boeing must mitigate.” Citing two sources familiar with the matter, Bloomberg reports that “data processing by a flight computer on the jetliner could cause the plane to dive in a way that pilots had difficulty recovering from in simulator tests.”

Boeing, for its part, has told Bloomberg that it agrees with the FAA’s finding and is working toward resolving the newly discovered safety risk, which is happening alongside a more expansive software redesign that’s been in the works for eight months.