A high-lift system on a wing with a curved nose and a leading-edge flap mounted via levers for movement between retracted and extended positions while expanding the airfoil profile, increasing its curvature and exposing a gap for guiding air from under the flap to above the wing. The levers form a four bar mechanism including first and second levers respectively pivotably connected at one end to spaced first and second points on the wing. The other ends of the levers are connected to opposite ends of a third lever forming part of the flap. The length and positions of the levers and the curvature of the wing nose are matched such that during initial extension from retracted position to an intermediate position the trailing edge of the flap blocks the gap between the flap and wing, and during further extension beyond the intermediate position the gap is exposed.