United Airlines tickets at zero cost because of a computer programming error will be allowed to use them, an airline spokeswoman said on Friday.

An error in the online reservation system “sold” airline tickets complimentary.

“United has reviewed the error that occurred yesterday and decided that, based on these specific circumstances, we will honor the tickets,” spokeswoman Mary Clark said in an email.

United did not say how many such tickets were issued on Thursday. The airline temporarily shut down its website to correct the error and also stopped booking flights through its phone center for about two hours.

Miscellaneous airport fees, such as the September 11 security fee, may have resulted in some passengers paying a nominal price for the tickets.