Wing of an aircraft having a mainplane (20), which has an upper face (22), a lower face (23) and an aerodynamically shaped area (21), and having an additional airfoil (10) which is articulated on the mainplane (20) and can be extended from a retracted state with a slot area (9) being opened between the mainplane (20) and the additional airfoil (10) and having a variable-position slot-varying apparatus (16) which is arranged on the lower face, forms a part of the aerodynamic profile of the additional airfoil (10) or mainplane (20) when the additional airfoil (10) is extended, and at least partially covers the slot area (9) between the mainplane (20) and the additional airfoil (10) on the lower face when the additional airfoil (10) is in the retracted state. The slot-varying apparatus (16) can be varied between a curved configuration, in which it forms a part of the aerodynamic profile of the additional airfoil (10) or mainplane (20) when the additional airfoil (10) is extended, and an extended configuration, in which it at least partially covers the slot area (9) between the mainplane (20) and the additional airfoil (10) on the lower face when the additional airfoil (10) is in the retracted state.