Methods, systems, and devices for wireless communications are described. An encoder of a wireless device may receive a number of information bits and a block size for transmission. If the block size is not a power of two, the encoder may round the block size up to the nearest power of 2, generate a larger codeword, and puncture the excess bits. The punctured bits may affect a rate of polarization when generating a polar code, and sub-blocks with a high number of punctured bits may produce too few sufficiently polarized channels. The encoder may implement a capacity backoff when polar coding to identify a greater number of polarized channels. The encoder may assign information bits to sufficiently polarized channels of the greater number of polarized channels.