The molecular mechanisms that build and power the mitotic spindle in vascular plants are not well understood. In animals and fungi, the balance of forces provided by motor proteins is crucially important, and kinesin-5 motors (motors that move towards microtubule plus ends) provide outwardly directed forces that are essential for spindle integrity. On p. 2819, Tobias Baskin and colleagues turn their attention to the roles of a kinesin-5 motor protein – AtKRP125c – in vascular plants. Using GFP-labelled AtKRP125c, they find that the protein localises to all microtubule arrays throughout the cell cycle, and analysis of a conditional mutant shows that AtKRP125c has an important role stabilising the mitotic spindle. Unusually for a kinesin-5, AtKRP125c also appears to function in interphase – the researchers observed AtKRP125c localising to interphase microtubules and found that these microtubules are disorganized in the mutant. The spindle architecture of kinesin-5-defective cells is similar in plants, animals and fungi. The motor's mitotic function therefore appears to be widely conserved, but plants take advantage of its activity in interphase as well.