The coupling of the electroweak gauge bosons of the Standard Model (SM) to leptons is independent of the lepton flavour. Extensions of the SM do not necessarily respect this lepton flavour universality. Semileptonic rare decays of heavy flavour, to which new particles can give sizeable contributions, allow for sensitive tests of lepton flavour universality, and constitute powerful indirect searches for phenomena beyond the SM. Of particular interest are rare $b\to sll$ decays that are readily accessible at the LHCb experiment. Recent results from LHCb on lepton flavour universality in rare $b\to sll$ decays are discussed.