One or more blades for a wind turbine have at least one guide vane (20) having a vane leading edge (22) and vane trailing edge (23), arranged in such that the guide vane (20) is substantially placed over a blade surface (8) of a suction side (16) of the blade (1) and extends in longitudinal direction (5) at least partly along the surface (8) of the root segment (12), wherein a line between the vane leading edge (22), the longitudinal axis (5) of the blade (1) and the chord (3) form at least one starting angle (β), and further wherein a second starting angle (βII) in the transition portion (14) is greater than a first starting angle (βI) in the plain portion (13) and less than a third starting angle (βIII) in the profiled portion (15).