185Re,187Re-NQR-spectra of polycrystalline NH4ReO4 and ND4ReO4 show a strong temperature dependence of their transition frequencies with anomalous positive temperature coefficients in contrast to the behaviour of other measured perrhenates. The positive values of the temperature coefficients are explained by an additional intermolecular interaction of the cations with ReO4-, which strengthens the intramolecular mechanism of reducing π-bond character with temperature.