Re-domestication of potato into an inbred line-based diploid crop propagated by seed represents a promising alternative to traditional clonal propagation of tetraploid potato, but self-incompatibility has hindered the development of inbred lines. To address this problem, we created self-compatible diploid potatoes by knocking out the self-incompatibility gene S-RNase using the CRISPR-Cas9 system. This strategy opens new avenues for diploid potato breeding and will also be useful for studying other self-incompatible crops.