Abstract: A blowout preventer operator locking system comprises a piston rod having one end coupled to a closure member. The operator further comprises an operator housing having one end coupled to a bonnet and a second end coupled to a head. The piston rod extends through the bonnet onto the operator housing where it is coupled to a piston that is disposed within the operator housing. The piston comprises a body and a flange. A sleeve is slidingly disposed within a cavity disposed within the piston and is rotationally fixed relative to the piston. A lock rod is rotatably coupled to the head and is threadedly engaged with the sleeve so that rotation of the lock rod axially translates the sleeve relative to the piston.