Assembly of - a screen device, comprising ∘ a screen which is able to be rolled up onto and unrolled from a screen roller in order to cover a window or a door; and ∘ a screen casing which extends substantially along a length direction and in which this screen roller is accommodated so as to be able to rotate; - a structure in which the window or the door is installed; and - fastening means for fastening the screen casing to the structure; wherein the fastening means: - comprise first hook-on elements which are provided on the screen casing; and - comprise a plurality of hook-on brackets (10, 11, 44, 45) which are fastenable distributed over the length direction of the screen casing to the first hook-on elements, wherein each hook-on bracket (10, 11, 44, 45): ∘ comprises a hook-on leg: - which extends substantially in a first plane; and - which is provided with second hook-on elements for thereon hooking of the first hook-on elements in order to fasten the hook-on bracket (10, 11, 44, 45) to the first hook-on elements; and ∘ comprises a fastening leg: - which extends substantially in a second plane (B, C) that deviates from the first plane; and - which is provided for fastening the hook-on bracket (10, 11, 44, 45) to the structure; characterized in that in the fastened state, the fastening leg extends away from the screen casing. - a screen device, comprising ∘ a screen which is able to be rolled up onto and unrolled from a screen roller in order to cover a window or a door; and ∘ a screen casing which extends substantially along a length direction and in which this screen roller is accommodated so as to be able to rotate; ∘ a screen which is able to be rolled up onto and unrolled from a screen roller in order to cover a window or a door; and ∘ a screen casing which extends substantially along a length direction and in which this screen roller is accommodated so as to be able to rotate; - a structure in which the window or the door is installed; and - fastening means for fastening the screen casing to the structure; - comprise first hook-on elements which are provided on the screen casing; and - comprise a plurality of hook-on brackets (10, 11, 44, 45) which are fastenable distributed over the length direction of the screen casing to the first hook-on elements, wherein each hook-on bracket (10, 11, 44, 45): ∘ comprises a hook-on leg: - which extends substantially in a first plane; and - which is provided with second hook-on elements for thereon hooking of the first hook-on elements in order to fasten the hook-on bracket (10, 11, 44, 45) to the first hook-on elements; and ∘ comprises a fastening leg: - which extends substantially in a second plane (B, C) that deviates from the first plane; and - which is provided for fastening the hook-on bracket (10, 11, 44, 45) to the structure; ∘ comprises a hook-on leg: - which extends substantially in a first plane; and - which is provided with second hook-on elements for thereon hooking of the first hook-on elements in order to fasten the hook-on bracket (10, 11, 44, 45) to the first hook-on elements; and - which extends substantially in a first plane; and - which is provided with second hook-on elements for thereon hooking of the first hook-on elements in order to fasten the hook-on bracket (10, 11, 44, 45) to the first hook-on elements; and ∘ comprises a fastening leg: - which extends substantially in a second plane (B, C) that deviates from the first plane; and - which is provided for fastening the hook-on bracket (10, 11, 44, 45) to the structure; - which extends substantially in a second plane (B, C) that deviates from the first plane; and - which is provided for fastening the hook-on bracket (10, 11, 44, 45) to the structure;