United Airlines came through on a promise it made almost 20 years ago.

Last month, John Walker discovered a United ticket in a box underneath his bed, WFMY2 reported. The ticket, for a flight from Nashville to Sacramento, was dated December 31, 1998.

The ticket was still attached to a letter that detailed the conditions of use, saying “domestic wholly unused non-refundable ticket(s) can forever be applied toward the purchase of another domestic non-refundable ticket, for the customer named on the ticket."

So 19 years later, “forever” was still applicable.

More From Travel + Leisure

Walker contacted United customer service, who transferred him to several different agents — none of whom were exactly sure what to do with a paper ticket. They hadn't been used in at least 10 years.

Finally, Walker reached out on Twitter to talk with a customer service agent. That agent told him that when United went bankrupt in 2010, they were absolved of all their outstanding debts — including “forever” airline tickets.

However, because Walker’s situation was so unique, the airline agreed to honor its “forever” promise.

“They decided to honor it partly because of the letter even though it wasn’t legally binding,” Walker told the local CBS News affiliate. “But also, because I think it was just good customer service on their part.”

Walker sent his old ticket to United as proof and is awaiting the arrival of a digital voucher for $378, the original cost of the 1998 flight.