A disruption to a system housing United Airlines’ flight information that caused more than 1,000 delays has been resolved.

United Airlines flight schedules are gradually returning to normal after a nationwide technical issue forced flight cancellations and delays Wednesday night. Residual delays and cancellations continued Thursday morning for United Airlines flyers at Chicago’s O’Hare International Airport after one of the airline’s computer systems went down Wednesday night,

An undisclosed “technology issue” delayed more than 1,000 United Airlines flights across the U.S. United Airlines said in a statement Wednesday that flights on major routes were held at their departure airports because of a technology issue.