KIC 1571511 is a 14-d eclipsing binary (EB) in the Kepler data set. The secondary of this EB is a very low mass star with a mass of and a radius of (statistical errors only). The overall system parameters make KIC 1571511B an ideal ‘benchmark object’: among the smallest, lightest and best-described stars known, smaller even than some known exoplanet. Currently available photometry encompasses only a small part of the total: future Kepler data releases promise to constrain many of the properties of KIC 1571511B to unprecedented level. However, as in many spectroscopic single-lined systems, the current error budget is dominated by the modelling errors of the primary and not by the above statistical errors. We conclude that detecting the RV signal of the secondary component is crucial to achieving the full potential of this possible benchmark object for the study of low-mass stars.