The invention relates to a navigation system for a motor vehicle for ascertaining a navigation position, having: a plurality of receivers for receiving respective position data of a plurality of different navigation satellite systems, an inertial measuring unit for ascertaining an inertial position of the navigation system, a receiving unit for receiving correction data, an additional receiving unit for receiving certified position data, a device which is coupled to the plurality of receivers, the inertial measuring unit, the receiving unit, and the additional receiving unit so as to transmit signals, wherein the device is designed to ascertain the navigation position on the basis of the position data, the inertial position, the correction data, and the certified position data. The invention additionally relates to a method which can be carried out by the navigation device in particular.