A serrated panel (70) for a wind turbine blade is disclosed. The panel (70) is configured to be attached to the trailing edge of a blade to form a plurality of serrations (71) at the trailing edge of the blade. The serrated panel comprises a base part (72) for attaching the panel (70) to the trailing edge of the blade. An exterior surface (78) of the base part comprises a corrugated surface in direction between longitudinal ends of the panel such that the exterior surface comprises crests (82) aligned substantially with midpoints of bases (80) of the serrations (71) and valleys (83) aligned substantially between serrations (71).