A tensioning assembly for use on a roller door, the roller door including a curtain windable on a roller for selectively blocking and unblocking a doorway above a floor surface, the tensioning assembly including: a drum attached to the roller for rotation therewith, a pulley disposed adjacent to the floor and also adjacent to a vertical edge of the curtain in the doorway blocking position; and a resilient member having a first end connected to the drum and a second end attached to a leading edge of the curtain, the resilient member passes around the pulley intermediate its first and second ends, and the resilient member is windable on the drum in an opposite sense to the winding of the curtain on the roller, the drum and resilient member are dimensioned relative to the roller and curtain to maintain a proportional stretch on the belt for all vertical positions of the curtain, thereby maintaining the curtain under tension at all times.