CRISPR-Cas9-based base editing allows precise base editing to achieve conversion of adenosine to guanine or cytosine to thymidine. In this issue of Cell, McAuley et al. use adenine base editing to correct a single base-pair mutation causing human CD3d deficiency, demonstrating superior efficiency of genetic correction with reduced undesired genetic alterations compared with standard CRISPR-Cas9 editing.