A screening device, such as a roller shutter, for mounting on the side of a roof window facing the exterior when the roof window is mounted in a roof construction, the roof window comprising a frame and a sash, and the screening device comprising: a top element and two side rails (17, 18), the two side rails (17, 18) each having a longitudinal slot (172, 182), a screening body, such as a roller shutter body comprising a plurality of slats, the screening body having mutually opposite side sections being guided in the longitudinal slots (172, 182) of the respective side rails (17, 18), and at least one gliding bracket (23, 24), the two side rails (17, 18) further comprising a guide channel (171, 181) for the at least one gliding bracket (23, 24), a first part (231, 241) of the at least one gliding bracket (23, 24) being adapted for being mounted at or on a bottom part of the sash of the window, the screening device further comprising a bracket system for mounting the top element of the screening device on the roof window, characterized in that the bracket system comprises two mounting brackets, each mounting bracket comprising a first bracket part and a second bracket part, the first bracket part comprising a section for mounting the first bracket part on the roof window, the first bracket part further comprising means for connection or being connected to corresponding means of the second bracket part in such a way that the second bracket part is rotatable with respect to the first bracket part when opening the roof window, the second bracket part comprises an element for attachment to the side rail (17, 18), the second bracket part further comprises a reception element for reception of a corresponding reception element (141, 142) provided on a side wall (145, 146) of the top element, and the top element being adapted for being locked with respect to the side rails (17, 18). a top element and two side rails (17, 18), the two side rails (17, 18) each having a longitudinal slot (172, 182), a screening body, such as a roller shutter body comprising a plurality of slats, the screening body having mutually opposite side sections being guided in the longitudinal slots (172, 182) of the respective side rails (17, 18), and at least one gliding bracket (23, 24), the two side rails (17, 18) further comprising a guide channel (171, 181) for the at least one gliding bracket (23, 24), a first part (231, 241) of the at least one gliding bracket (23, 24) being adapted for being mounted at or on a bottom part of the sash of the window, the screening device further comprising a bracket system for mounting the top element of the screening device on the roof window, characterized in that the bracket system comprises two mounting brackets, each mounting bracket comprising a first bracket part and a second bracket part, the first bracket part comprising a section for mounting the first bracket part on the roof window, the first bracket part further comprising means for connection or being connected to corresponding means of the second bracket part in such a way that the second bracket part is rotatable with respect to the first bracket part when opening the roof window, the second bracket part comprises an element for attachment to the side rail (17, 18), the second bracket part further comprises a reception element for reception of a corresponding reception element (141, 142) provided on a side wall (145, 146) of the top element, and the top element being adapted for being locked with respect to the side rails (17, 18).