The LHCb detector is designed for the study of b-hadron and c-hadron decays, using proton-proton collisions provided by the LHC. In order to achieve these physics goals, the trajectories of stable charged particles (tracks) need to be reconstructed accurately and with a high and well-known efficiency. The precise knowledge of this charged-particle reconstruction efficiency is essential in measurements of branching fractions, for example. While muons produced in heavy flavour decays are nearly unhindered by the LHCb detector material, electrons suffer from energy loss via bremsstrahlung. In some cases, the energy loss affects the trajectory to such a degree that the electrons no longer traverse all tracking detectors. Therefore, the track-reconstruction efficiency for electrons describes not only the performance of the trackreconstruction algorithms for electrons, but also the impact of this loss in geometrical acceptance. Thus far, no direct measurement of the electron reconstruction efficiency at LHCb exists. Tests of lepton universality in b→ sll (l= µ, e) transitions (eg refs.[1–3]) have estimated the efficiency difference between muons and electrons using simulation. This estimate is validated by measuring the ratio of branching fractions B (J/ψ→ e+ e−)/B (J/ψ→ µ+ µ−), which is constrained by theory and external measurements to unity. A measurement of the single electron efficiency is not only