The invention relates to an ankle orthosis comprising a U-shaped support stirrup made of a flexible material, the sides of which stirrup converge beneath the foot in a web projecting as a tab toward the metatarsus, extend past the bones, and are held together at their end regions by a fastening strap wrapping around the leg. The tab has a convexity, which presses against the cuboid bone of the foot due to a preloading of the tab.