A method of correcting a pitch angle deviation of a blade of a wind turbine is provided. First blade load measurements measured when the wind turbine was operating in a first operational mode are provided, and used to determine calibration parameters. Second blade load measurements measured when the wind turbine was operating in a second operational mode are provided, and the calibration parameters applied to determine calibrated blade load measurements. A pitch angle deviation of at least one blade of the turbine is estimated based on an identified difference between the calibrated blade load measurements, and a pitch angle is adjusted to correct for the pitch angle deviation.