A milling machine includes a rotor drive transmission having a plurality of gears disposed between a prime mover and a cutting rotor. The rotor drive transmission is associated with a rotor transmission hydraulic circuit including a hydraulic gearshift actuator to engage the plurality of gears in one or more gear ratios and a gearshift directional control valve to direct hydraulic fluid to and from the hydraulic gearshift actuator. In occurrence of a fault condition, the rotor transmission hydraulic circuit includes a gearshift trapping valve to maintain hydraulic pressure in the hydraulic gear actuator and the engaged gear ratio of the rotor drive transmission.