Belt tensioner

The invention relates to a belt tensioner, in particular a rotary tensioner, for a safety belt, comprising an elongated, preferably cylindrical pressure container (12); a piston which is arranged in the pressure container (12) in a movable manner in the longitudinal direction and which can be supplied with a pressurized fluid and can thereby be moved in a tensioning direction; a pushing means (20) which interacts with the piston; and a stop (24) which is provided on the inner face (38) of the pressure container (12) and against which the piston (18) can rest in the tensioning direction in an end position, wherein the piston seals the pressure container (12) in said end position. The stop (24) consists of a plastically deformable material and is plastically deformed by the piston (18) in the end position such that the piston sealingly sits against the inner face of the pressure container (12).