The structure of the transition metal oxide V6O13, a potential cathode material in lithium-polymer batteries, has been studied at 95 K using single-crystal X-ray diffraction (XRD). A phase transition has been determined by differential scanning calorimetry (DSC) measurements to occur at 153 K, with a heat of transition of -1.98 kJ mol(-1). In this low-temperature phase, the V and O atoms move by up to 0.21 A out of the mirror plane they occupy in the room-temperature structure. It is concluded that the earlier reported space group P2(1)/a [Kawada et al. (1978). Acta Cryst. B34, 1037-1039] is incorrect and that a more appropriate choice of space group is Pc.