Boeing suspended deliveries of the planes in May while the Federal Aviation Administration reviewed its method for evaluating the aircraft. The issue arose after Boeing said last year there was incorrect spacing on some 787 parts, including the fuselage.
Regulators said Monday that the new defect was detected "near the nose" of certain 787s that Boeing has put together but not yet delivered.
"The company has been engaged in detailed discussions with the FAA on verification methodology for 787 fuselages, and conducting associated inspections and rework," Boeing said in a statement.
"In connection with these efforts, the company has identified additional rework that will be required on undelivered 787s."
Boeing said it will reprioritize production resources to aid in the inspection of 787s over the coming weeks.
"As that work is performed, the 787 production rate will temporarily be lower than five per month," the company added.
"Boeing now expects to deliver fewer than half of the 787s currently in inventory this year."
The FAA has said the defect does not pose a threat to the flying public.
"Boeing has committed to fixing these airplanes before resuming deliveries," the regulator said, according to CNBC.
Boeing has only recently returned its 737 Max to skies worldwide. That model was grounded for almost two years after a problem with the automated flight software contributed to two crashes overseas in 2018 and 2019.
