Abstract: A reflector sight for a firearm, comprises an adjustment assembly for adjusting the location of a reticule within the field of view. The adjustment assembly comprises: a pair of vertical and horizontal adjustment screws; and a carrier body associated with a reticule generator, the carrier body having a pair of mutually perpendicular channels within which respective substantially cylindrical barrel nuts for the pair of adjustment screws are located. Each channel is configured to allow longitudinal movement of its respective barrel nut along the channel but relative movement perpendicular thereto is constrained, such that rotation of the adjustment screws can move the carrier in the horizontal and vertical directions without requiring any axial movement of the adjustment screws.