Disclosed is a locking unit having a piston and serving for locking the movement of the piston which can be acted on with pressure of a fluid. The locking unit can additionally have an electromagnet and at least one detent element. The detent element interacts with an armature or an armature rod of the electromagnet, and the piston has at least one detent receptacle, where the piston can be secured by the retaining interaction of the detent element with the detent receptacle. The piston is adjustable between a retracted position and an extended position. The piston is mounted at least partially in a middle piece which is surrounded at least partially by a housing, and the middle piece is configured in two parts from a metal part and a plastic part.