An external screening arrangement configured to assume a mounted condition on a roof window, the roof window having a window opening, a frame structure and a sash structure extending in parallel to the roof surface, each with top (3a, 4a) and bottom members (3d, 4d) and two mutually parallel side members (3b, 3c, 4b, 4c), wherein the screening arrangement comprises: a screening body having two side edges and a predefined length between a first end portion and a second end portion, said screening body being movable, in the mounted condition of the screening arrangement, in a longitudinal direction between a non-screening position and a number of screening positions in which the screening body at least partially covers the window opening, a top casing configured to extend substantially in parallel with the top member of the frame in the mounted condition, a roller shaft accommodated in the top casing and connected to drive means, the drive means being configured to rotate the roller shaft in a winding direction and an unwinding direction, the first end portion of the screening body being connected to the roller shaft such that the screening body is wound on the roller shaft in the non-screening position, a bottom profile extending substantially in parallel with the top casing between two ends and connected to the second end portion of the screening body, two side rails (21, 22) configured to extend substantially in parallel with a respective side member of the frame and sash structure in the mounted condition to guide at least the ends of the bottom profile, a set of side covers configured to be connected to the frame structure of the roof window, and a positioning device to provide at least temporary, releasable engagement with engagement means of the respective side cover, characterised in that said positioning device comprises a clip providing snap engagement with the engagement means of the side cover, and in that said positioning device is configured to be fastened to the roof window in the mounted condition of the screening arrangement. a screening body having two side edges and a predefined length between a first end portion and a second end portion, said screening body being movable, in the mounted condition of the screening arrangement, in a longitudinal direction between a non-screening position and a number of screening positions in which the screening body at least partially covers the window opening, a top casing configured to extend substantially in parallel with the top member of the frame in the mounted condition, a roller shaft accommodated in the top casing and connected to drive means, the drive means being configured to rotate the roller shaft in a winding direction and an unwinding direction, the first end portion of the screening body being connected to the roller shaft such that the screening body is wound on the roller shaft in the non-screening position, a bottom profile extending substantially in parallel with the top casing between two ends and connected to the second end portion of the screening body, two side rails (21, 22) configured to extend substantially in parallel with a respective side member of the frame and sash structure in the mounted condition to guide at least the ends of the bottom profile, a set of side covers configured to be connected to the frame structure of the roof window, and a positioning device to provide at least temporary, releasable engagement with engagement means of the respective side cover, characterised in that said positioning device comprises a clip providing snap engagement with the engagement means of the side cover, and in that said positioning device is configured to be fastened to the roof window in the mounted condition of the screening arrangement.