[en] Hyperfine spectra are reported for Er present as a dilute impurity in the fluorite structure compound delta-ZrH₁₅ and the tetragonally distorted fluorite epsilon-ZrH₁₈₇. In both cases, the hyperfine spectra are identical and show cubic symmetry around the Er ion regardless of the host crystal structure, showing the formation of a locally cubic Er-hydrogen cluster. Paramagnetic relaxation frequencies are also identical in the two phases, in spite of large changes in the electronic density of states. Mechanisms for the formation of such Er-hydrogen clusters are discussed