A fuel filling neck includes a closure flap pivotably mounted thereon to be pivoted between a neck closed position and a neck open position. The flap is preloaded into the closed position by spring pretension. A mis-filling prevention device is in the filling neck between the closure flap and an insertion opening for a fuel pump nozzle and has a closed position that prevents the closure flap from being pivoted into the open position, and an enabling position permitting the closure flap to be pivoted into the open position. The mis-filling prevention device is mounted with axial play so as to be first axially forced against the closure flap by the fuel pump nozzle as the nozzle is inserted, the closure flap being moved into a partly open position, and, during subsequent further insertion of the nozzle, the mis-filling prevention device being moved into the enabling position.