A method of detecting an adjustment fault related to a wind turbine rotor blade mounted at a wind turbine rotor and including an adaptable flow regulating device, in particular spoiler and/or flap, the method including: estimating a quantity indicative of a change of a driving impact of wind on the wind turbine rotor based on at least two settings of the adaptable flow regulating device; determining another quantity indicative of a desired change of the driving impact on the wind turbine rotor, in order to change a value of a rotor speed to a reference value of the rotor speed; and indicating an adjustment fault based on a comparison of the quantity with the other quantity, is provided.