International audienceWe report the first result from a dark photon dark matter search in the mass range from 78.62 to 83.95μeV/c2 with a dielectric haloscope prototype for MADMAX (Magnetized Disc and Mirror Axion eXperiment). Putative dark photons would convert to observable photons within a stack consisting of three sapphire disks and a mirror. The emitted power of this system is received by an antenna and successively digitized using a low-noise receiver. No dark photon signal has been observed. Assuming unpolarized dark photon dark matter with a local density of ρχ=0.3GeV/cm3 we exclude a dark photon to photon mixing parameter χ>3.0×10−12 over the full mass range and χ>1.2×10−13 at a mass of 80.57μeV/c2 with a 95% confidence level. This is the first physics result from a MADMAX prototype and exceeds previous constraints on χ in this mass range by up to almost three orders of magnitude