A robot controller is adapted to execute a program an indication of a setpoint speed of a robot arm, an indication of a contemporaneous setpoint fluid flow per unit time of a spray gun supported by the robot arm, and an indication of a contemporaneous further setpoint quantity of the spray gun. The robot controller is configured to obtain an estimate of actual speed of the robot arm; determine whether the estimate deviates from the setpoint speed; and, in case of a deviation, adjust the setpoint fluid flow per unit time in accordance with a first compensation function. In an embodiment, the robot controller is further configured to concurrently adjust, in case of a deviation, the further setpoint quantity in accordance with a second compensation function, which is different from the first compensation function.