In a control system and a method for operating a permanent-magnet electrical machine, when the electrical machine is switched off after one of a functional computer and a monitoring computer of the control system has identified a fault, in order to reduce the braking torque of the electrical machine, which is switched-off but still rotating an output stage of the control system is subjected to a three-phase short circuit if the rotation speed D1 does not fall below a definable limit value GR1 or if a voltage U_DC of the output stage (2) exceeds a limit value Umax, and when the rotation speed D1 is below the definable limit value GR1 and a voltage U_DC of the output stage does not exceed a limit value Umax, all the circuits breakers (2o1, 2o2, 2o3 2u1, 2u2, 2u3) of the output stage (2) are opened in order to fully disconnect the electrical machine from the output stage.