The invention relates to a belt tensioner (30) for a vehicle occupant restraint system comprising a housing (32), a working chamber (34) into which the compressed gas released in the case of restraint is flowing, a pull rope (24) extending through an opening (36) within the housing (32) and a sealing bush (10) for sealing the working chamber (34) against the opening (36) between the pull rope (24) and the housing (32), with the sealing bush (10) comprising a sleeve (16) and a sealing element (12) and the sealing bush (10) being pressed onto the pull rope (24) by plastic deforming of the outer sleeve (16).