The invention relates to a self-propelled working machine, preferably in the form of a dumper truck or truck, having an electric drive comprising at least one electric motor (4), a generator (5) driven by a combustion engine (6) for supplying power to the electric drive, and a braking device (4, 11) for braking the working machine. Said braking device provides power-generating braking via the electric drive (4) and a feed-back of electrical engine braking power of the electric motor (4) to the generator (5), in order to support the engine braking power provided by the combustion engine (6). The invention also relates to a method for braking a working machine of this type. According to the invention, a braking control device is provided to automatically engage a mechanical brake (11) in accordance with the engine braking power fed back to the combustion engine and/or in accordance with the operating state of the combustion engine supplied with fed-back engine braking power.