A device (1) for separating regions of a space, with at least one ceiling rail (3) for pressing on the ceiling (4) of the space, with at least one wall rail for making contact with the wall (7) of the space and with at least one floor rail (8) for resting on the floor (9) of the space. In order to prevent passage of dust through the separated region of the space, there is least one diagonal brace (36) for detachable mounting on the wall rail (5) and the floor rail (8) outside of the corner region (37) between the wall rail (5) and the floor rail (8) and for applying pressure to the middle region (38) of the wall rail (5) and that the diagonal brace (36) has a length which is greater than half the length of the wall rail (5).