Abstract: A tensioning device for the corner joints of a fabric stretcher that provides for incremental movement of each stretcher member at the corner joint for mitered, butt-end, or overlapping corner joints. The device includes first and second rigid channels each shaped in a right angle joined end to end to form a corner joint support. Each rigid member includes elongated apertures through which fasteners allow for rigid connection of the device to the stretcher members. Tensioning devices such as bolts or screws protrude through the bottom support members on each side to allow for individual tensioning against the frame member. In one embodiment the first and second right angled channels are themselves offset from the plane of the stretched fabric through the back support members to allow for lean-in of the stretcher members.