CHICAGO (CBS) — United Airlines will eat the cost of free fares many passengers were able to book on Thursday, thanks to a mistake on the airline’s online reservation system.

Friday afternoon, the airline said it would honor tickets sold for $0 fares, plus $5 to $10 in taxes and fees for many flights.

The airline said there was an error on the United reservation system on Thursday, resulting in the free fares. United has since fixed the mistake, but not before many customers took advantage of the free fares.

United might not have had a choice in the matter. U.S. Department of Transportation policy indicates airlines must honor any tickets once a purchase has been confirmed, even if the price was incorrect, and may not increase prices after the customer receives a confirmation.

Travel blogs heated up when the mistake was discovered, and untold numbers of travelers scooped up the free fares to book flights. After discovering the error, United shut down the reservation system to correct the prices.

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