According to the Raleigh News and Observer:
Republicans successfully overrode Gov. Bev Perdue’s veto of a fracking bill during a quick vote taken just after 11 p.m. Monday.
The override effort gained the 72 votes necessary only because a Democrat accidentally voted for it and was not allowed to change. Immediately when Rep. Becky Carney of Mecklenburg County said she’d like to change her vote, Republican Rep. Paul Stam of Wake County called for a procedural vote to prevent vote changes. Under normal circumstances vote changes are routine.
The procedural vote gained 71 votes, enough to lock in the first vote but also showing that the Republicans lacked enough votes for a veto had Carney not pressed the wrong button.