Asymmetric division of a stem cell generates another self-renewing stem cell and a differentiating daughter cell. How this differential acquisition of cell fates is established and regulated is so far poorly understood. In their previous study, Chen and colleagues reported that upon division of fly male germline stem cells, histone H3 was asymmetrically distributed, with the stem cell retaining the 'old' pool of these histones. Now, the group has demonstrated that this histone asymmetry is established by transient phosphorylation of 'old' histones, occurring upon mitotic entry. They also showed that perturbation of this phosphorylation had severe consequences, including infertility and tumorigenesis. Altogether, the authors revealed that histone H3 phosphorylation enables discrimination between sister chromatids destined for stem cells versus differentiating progeny, and this ensures proper functioning of the stem cell compartment.