An example device applies a primary transform to a current block of video data to create primary transform coefficients. The device determines whether intra sub-partitioning is applied to the current block of video data. The device applies a primary transform to the current block. The device also determines whether a primary transform size for the current block of video data is at least a predetermined size. Based on intra sub-partitioning being applied and the primary transform size being at least the predetermined size, the device applies a secondary transform to primary transform coefficients and codes the current block of video data based on the secondary transform.