Boeing is facing even more problems related to its embattled 737 MAX planes—this time, after an employee found improperly drilled holes on the jet’s fuselages, according to The Wall Street Journal. The aerospace giant has since been forced to rework at least 50 737 MAX jets still under construction, the newspaper reported Sunday. Some of the company’s deliveries will likely be delayed, but planes that have already been cleared to fly can continue to carry passengers, Boeing Commercial Airlines President Stan Deal said in a memo to employees. “This is the only course of action given our commitment to deliver perfect airplanes every time,” he wrote. The fuselages were made by Spirit Aerosystems, a supplier that’s been behind other quality control issues dogging the 737 MAX.