We report the discovery of a linear relationship between the root mean square (rms) variability amplitude and the mean flux in the accreting white dwarf binary system MV Lyrae. Our light curve, obtained with the Kepler satellite, spans 633 d with quasi-continuous 58.8-s cadence resolution. We show, for the first time, that how this cataclysmic variable displays linear rms–flux relations similar to those observed in many other black hole binaries, neutron star binaries and active galactic nuclei. The phenomenological similarity between the rms–flux relation observed here and in other X-ray binaries suggests a common physical origin for the broad-band variability, independent of source type, mass or size of the compact accretor. Furthermore, we infer the viscosity parameter, α, and disc scale height, H/R, using two independent methods. In both cases, both values are found to be uncomfortably high to be accommodated by the disc instability model.