A round baler is provided with a bale-forming chamber and boundary apparatus of the bale-forming chamber that can be moved into an open position for ejecting a completed bale. The boundary apparatus includes a pivoting part rotatable between a first position, a second position and a third position. The axial dimensions of the bale-forming chamber can be changed by at least one side wall that can be moved by an adjustment drive. The adjustment drive is configured such that the axial dimensions of the bale-forming chamber increases when the pivoting part rotates to the second position and then reduces when the pivoting part rotates to the third position.