This invention relates to a safety belt for fastening a person in a chair of a vehicle, which chair has such a construction that the attachment of the back of the chair of the vehicle when loaded more than to a certain level can collapse, whereby the back of the chair can move backwards in relation to the vehicle, the safety belt in a conventional way being a multipoint belt comprising a portion which is intended to be in contact with the stomach of the person. According to the invention the safety belt is characterized by the fact that the mentioned portion of the belt has the ability to apply a force against the stomach of the person that is greater than normally, which in combination with the ability of the back of the chair of the vehicle to be displaced backwards forces the person in question backwards in relation to the vehicle.