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 which are fastenable distributed over the length direction of the screen casing to the first hook-on elements , wherein each hook-on bracket : ∘ comprises a hook-on leg : - which extends substantially in a first plane (A); 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 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 (A); and - which is provided for fastening the hook-on bracket 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 which are fastenable distributed over the length direction of the screen casing to the first hook-on elements , wherein each hook-on bracket : ∘ comprises a hook-on leg : - which extends substantially in a first plane (A); 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 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 (A); and - which is provided for fastening the hook-on bracket to the structure ; ∘ comprises a hook-on leg : - which extends substantially in a first plane (A); 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 to the first hook-on elements ; and - which extends substantially in a first plane (A); 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 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 (A); and - which is provided for fastening the hook-on bracket to the structure ; - which extends substantially in a second plane (B, C) that deviates from the first plane (A); and - which is provided for fastening the hook-on bracket to the structure ; <EOS>