An adjustment device for adjusting a longitudinal position of a vehicle seat, comprises: a first guide rail; a spindle fixed to the first guide rail and extending along a longitudinal axis; a second guide rail being linearly movable along the longitudinal axis with respect to the first guide rail, the second guide rail having a base and a first leg extending from the base; and a gearing fixed to the second guide rail and having a housing, the gearing being in operative connection with the spindle to move the second guide rail relative to the first guide rail. At least one support member is arranged on the second guide rail, the at least one support member having a support face extending transversely to the longitudinal axis and facing the housing of the gearing for supporting the gearing with respect to the second guide rail. The support face comprises a first edge facing the base or the first leg and having a welding section via which the first edge is fixed to the base or the first leg by welding, a tab protruding from said first edge and engaging with an opening of said base or said first leg.