A migrating cell must establish front-to-back polarity in order to move. In this issue, Juanes-Garcia et al. (2015. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201407059) report that a short serine-rich motif in nonmuscle myosin IIB is required to establish the cell's rear. This motif represents a new paradigm for what determines directional cell migration.