The adapter is formed in two parts using an adapter rail (1) and an adapter angled bracket (4). The adapter rail has a double T-profile, and on one side is dimensioned to match the insertion clearance for the roller shutter (2); the other side of the profile has a broad contact surface for the window (6). The shank of the adapter rail and a shank of the angled bracket are so dimensioned w.r.t. thickness that each is outstandingly mechanically stable.
