Lockheed Martin is to repay $265m, after over-billing the US Defence Department for the F-35 Joint Strike Fighter.
The accounting glitch, caused by a coding error in the company's accounts department, was discovered earlier this week and dates back to 2002.
The error affected invoices from subcontractors Northrop Grumman and BAE Systems, although Lockheed says the pair did not cause the glitch, and it has no effect on their accounts.
Lockheed says the money will be returned to the Pentagon promptly, and it is working out the appropriate rate of interest payable.
The error is not expected to have any effect on Lockheed's development schedule or the company's financial position.
Reported by Elizabeth Clifford-Marsh