In a method for controlling an operation of an electric motor, electric voltages applied to electric phases of the electric motor are generated and output in a modulation in a controlled manner dependent on a rotor position of the electric motor and a target/actual comparison of at least one first variable which characterizes a load on the electric motor or an actual rotational speed of the electric motor. A rotor position angle, which characterizes the rotor position, is complemented with a specified preliminary control angle and another regulated preliminary control angle component upon reaching a field weakening range of the electric motor so as to form a sum angle. The sum angle is used to characterize the rotor position in the modulation upon reaching the field weakening range. The disclosure also relates to a device for controlling an operation of an electric motor.