Cytokinesis is the process that separates two daughter cells after chromosome segregation. It involves the constriction of an actomyosin ring in the centre of the cell, which causes the formation of a cleavage furrow, but the molecular details of how these processes are connected remain poorly understood. Using fission yeast as a model organism, Maitreyi Das and colleagues (Onwubiko et al., 2019) investigate a double mutant that combines deletion of the Cdc42 activator gef1 (gef1Δ) with an activated mutant of the formin cdc12 (cdc12Δ503). These strains display an uneven localisation of the F-BAR protein Cdc15, which promotes ring constriction, at the actomyosin ring, resulting in it constricting in a non-concentric fashion. Moreover, activated Cdc12 causes reduced Cdc15 levels at the ring, a phenotype that is replicated by inhibition of the actin nucleator Arp2/3, which is required for endocytosis at the division site. Interestingly, gef1Δ and cdc12Δ503 cells both have defects in Cdc15 endocytosis, suggesting that this could be the origin of the abnormal Cdc15 distribution at the actomyosin ring. Furthermore, expression of constitutively active Cdc42 rescues the lack of Gef1 and restores normal Cdc15 dynamics at endocytic patches, indicating that Gef1 regulates Cdc15 through Cdc42. The authors also develop a mathematical model that establishes the conditions that lead to uneven distribution of Cdc15 at the ring, namely a low Cdc15 dissociation rate and a high number of Cdc15 molecules associated with endocytic patches. These findings thus implicate Gef1 as an endocytosis regulator that establishes an even Cdc15 distribution in the actomyosin ring, thereby promoting the uniform and timely formation of the concentric furrow.