A shutter mounting adjuster provided between a non-vertical peripheral wall of a shutter opening and a hanging strip hinged to a shutter to support the shutter in the shutter opening. A slider movably mounted in a longitudinal groove of the hanging strip of the shutter, and an arched spring strip fixed on the slider for movement with the slider along the longitudinal groove for enaging the non-vertical peripheral wall to postion the hanging strip vertically in the shutter opening.