A longitudinal adjuster for a vehicle seat may have a rail assembly having two rail pairs of seat rails. The respective rail pair has a fixed seat rail and a seat rail that is movable relative to the fixed seat rail. The rail assembly may also have a motor unit and a gearbox unit, which couples the motor unit and the movable seat rail. The rail assembly may also comprise a holder for receiving a gearbox housing of the gearbox unit. The holder is arranged with the gearbox unit in a hollow space formed by the one rail pair and is fixed to the movable seat rail. The holder is formed so as to be open at one end and closed at the opposite end. The holder has at least one stiffening element at the open end.