New gene-editing tools challenge conventional policy proscriptions of research aimed at either human germline gene editing or human enhancement by potentially lowering technical barriers to both kinds of intervention. Some recent gene-editing reports have begun to take up the prospect of germline editing, but most experts are in broad agreement that research should prioritize medical applications over attempts to enhance human traits. However, there is little consensus about what counts as human enhancement in this context, or how to deal with the issues it flags. Moreover, several influential reports interpret medical applications to include disease prevention as well as treatment as a goal for gene-editing research. This challenges the current policy consensus because using gene editing to prevent disease would incidentally facilitate human enhancement applications in a variety of ways. If such research efforts are penalized by policy concerns about enhancement, then their preventive health benefits could be lost. To avoid being caught off guard by such challenges, science policy makers will need to think more carefully about what ‘‘prevention’’ might mean in the gene-editing context, and develop research governance that can anticipate and address the human enhancement concerns it will raise. To accomplish the latter, the scope of policy making will need to expand from its narrow focus on human clinical trials to engage with basic researchers driving the translational pipeline toward preventive gene editing and the science policy makers who have to address its ‘‘off-label’’ uses.