A video decoding method according to the present document comprises the steps of: configuring an MPM list by deriving candidate intra prediction modes on the basis of a first neighboring block located on the left side and a second neighboring block located on the upper side with respect to the current block; deriving an intra prediction mode for the current block on the basis of the MPM list; generating prediction samples for the current block on the basis of the intra prediction mode; and generating a reconstructed picture for the current block on the basis of the prediction samples, wherein a first intra prediction mode of the first neighboring block and a second intra prediction mode of the second neighboring block are the same, wherein the candidate intra prediction modes including a DC mode are derived on the basis of a case where both the first intra prediction mode and the second intra prediction mode are the DC mode.