Cell Biology Centrioles are microtubule-based organelles composed of an archetypal cylindrical arrangement of tubulin. Centrioles duplicate when a daughter centriole grows from the side of the mother, but it has been unclear how daughters grow to the right size. Aydogan et al. used live-cell imaging to quantify the dynamics of daughter centriole assembly in developing Drosophila embryos. They found that Polo-like kinase 4 (Plk4) promoted incorporation of a centriole component, Sas-6, into the proximal end of the growing daughter at a linear rate during the early S phase. However, growth abruptly stopped when centrioles reached the correct size in the mid- to late S phase. Plk4 is a “suicidal” enzyme that promotes its own degradation, and it acted as a homeostatic clock to set the size of centrioles: The higher the centriolar Plk4 activity, the faster the centrioles would grow, but the faster Plk4 would become degraded and centriole growth would cease. J. Cell Biol. 10.1083/jcb.201801014 (2018).