The invention relates to a commercial vehicle seat with a seat portion, with a backrest portion and with a seat substructure for mounting on a body portion of a commercial vehicle, wherein said seat substructure has locking means for securing against an unintended rotary movement of a rotary adjustment means for rotating at least the seat portion relative to the body portion, wherein the locking means comprises a locking member that is supported so as to be translationally displaceable along a displacement axis, for fixing the rotary adjustment means, and wherein said locking member comprises a base body member secured against rotation about the displacement axis, the base body height of which base body member is at least two to four times, preferably more than six times smaller than the base body width thereof.