A frame assembly is disposed within an opening of a structure. The frame assembly includes first and second frame members each defining an interior and having a plurality of walls extending between a first end and a second end. The frame assembly includes a cornerlock extending into each of the first and second frame members. The cornerlock includes first and second body members each having hinge and distal ends and are rotatably coupled together at the hinge ends. The first body member has at least one arm deflectable to bias against and engage the first frame member. Each of the first and second frame members has a mitered end. The first and second frame members abut at the mitered ends in an angular configuration. The cornerlock rotates to correspond with the angular configuration and is entirely disposed within a combination of the interiors of the first and second frame members.