A controller (1) to reduce integral non-linearity errors of a magnetic rotary encoder (2) comprises a position error determining unit (20) to determine a plurality of time marks (P0, . . . , Pk) specifying a respective time at which a moving device (3) reaches a respective one of predefined positions (α0, . . . , αk). The position error determining unit (20) calculates a plurality of error correction parameters (B[0], . . . , B[k]) in dependence on the time marks (P0, . . . , Pk). An error compensation unit (10) of the controller determines a respective error compensated position parameter (φstart_comp, φ0_comp, . . . , φn_comp) for each position parameter (φstart, φ0, . . . , φn) received from the encoder (2) in dependence on the respective position parameter (φstart, φ0, . . . , φn) and the respective error correction parameter (B[0], . . . , B[k]).