Let k ⩾ 3 be a fixed integer. We exactly determine the asymptotic distribution of ln Zk(G(n, m)), where Zk(G(n, m)) is the number of k-colourings of the random graph G(n, m). A crucial observation to this end is that the fluctuations in the number of colourings can be attributed to the fluctuations in the number of small cycles in G(n, m). Our result holds for a wide range of average degrees, and for k exceeding a certain constant k0 it covers all average degrees up to the so-called condensation phase transition.