Boeing is investigating fuselage problems on its 787 Dreamliners

Boeing might have put together some of its planes incorrectly.

Reuters reports that company was investigating whether some of the fasteners on its 787 Dreamliner jetliners connecting the planes’ fuselages to their frames had been incorrectly installed, citing sources inside the company. It is not clear what effect the error would have had on plane safety.

In a statement to Quartz, the company confirmed that it was looking into the issue. “Our 787 team is checking fasteners in the side-of-body area of some undelivered 787 Dreamliner airplanes to ensure they meet our engineering specifications,” Boeing said. Neither Reuters nor Boeing said how many planes were affected.

Earlier this year, former Boeing engineer Sam Salehpour made headlines with claims that the skins on some 787 Dreamliners had been put on too unevenly and that many of the planes were in danger of ripping apart in mid-air. Between that plane and the 737 Max model — one of which lost a door plug mid-flight in January — quality issues and safety questions are surrounding models that make up nearly 90% of the plane manufacturer’s current order backlog.

“The in-service fleet can continue to safely operate,” Boeing said in its statement. “We are taking the time necessary to ensure all airplanes meet our delivery standards prior to delivery. We are working closely with our customers and the FAA and keeping them updated.”