Safety belt pretensioner

A tightener (10) for a safety belt, comprising a cylinder (12), a piston (14) which is arranged to be displaceable in the cylinder, a tension transmission means (24) which is connected to the piston in order to transmit the movement of the piston to the safety belt, and a drive (18) which can exert a driving force on the piston in order to tighten the safety belt, is characterized in that the piston (14) is provided with a deformation element at which the tension transmission means (24) acts.