Haspin is an atypical mitotic kinase that phosphorylates histone H3 on threonine 3 (H3T3), which is required to target Aurora B to centromeres. However, how Haspin is activated upon mitotic entry remained unknown. Two independent studies, published in Molecular Cell and in this issue of EMBO reports by Ghenoiu et al [1] and Zhou et al [2], respectively, now show that Plk1 is responsible for Haspin activation as a H3T3 kinase. These results shed light on the spatiotemporal regulation of Aurora B to ensure mitotic fidelity.