SpaceX has a problem, and it could cripple the private spaceflight company’s contracts with the federal government. Congressional investigators with the Government Accountability Office have let NASA’s administrators know that SpaceX might not be the best choice for future government missions, due to a tendency for the turbine blades inside the Falcon 9 rocket’s engines to crack under stress, according to the Wall Street Journal.

This defect is different from the fueling error one that likely caused a Falcon 9 to spectacularly explode on its launchpad. The Journal confronted SpaceX with its knowledge of the preliminary GAO report, which has not been released publicly, and published this reply from the company.

A SpaceX spokesman said “we have qualified our engines to be robust” to such cracks but are “modifying the design to avoid them altogether.” The pending changes “will be part of the final design” for the Falcon 9, he added, in partnership with NASA to qualify engines for manned spaceflight.”

The SpaceX spokesperson is hopefully referring to the upgraded Falcon 9 Block 5 rocket, the successor to the current model which is slated to begin production early this year. The company’s other workhorse in the next decade will be the Falcon Heavy, which is equipped to carry heavy payloads, including the company’s Dragon spacecraft, the vehicle SpaceX hopes to eventually send manned flights in. The Dragon also flies on standard Falcon 9 rockets, which is why the GAO is subjecting the company’s process to such scrutiny.

According to the Journal, Government officials have known about the turbine-cracking problems for “many months or even years,” and that the defects continued to show up in tests in September. NASA’s acting administrator Robert Lightfoot told the Journal that NASA was “talking to [SpaceX] about turbo machinery.” Fortunately, he also told the Journal “we know how to fix them,” although the fix could take some time if SpaceX has to switch to bigger parts.

Since the explosion last September, SpaceX has been rushing to catch up to a demanding launch schedule and prove to the government it’s worthy of taking on more missions, more money, and eventually, humans. The company hopes to launch a cargo mission to the ISS in mid-February. If nothing blows up, it might still have a shot at being NASA’s new taxi service to orbit.

Correction 2/4/16: This article’s headline has been updated.

Photos via Getty Images / NASA