Lithium-ion dynamics in the garnet-type solid electrolyte “Li7La3Zr2O12” (LLZ) crystallizing with cubic symmetry was probed by means of variable-temperature 7Li NMR spectroscopy and ac impedance measurements. Li jump rates of an Al-containing sample follow Arrhenius behaviour being characterized by a relatively high activation energy of 0.54(3) eV and a pre-exponential factor of 2.2(5) × 1013 s-1. The results resemble those which were quite recently obtained for an Al-free LLZ sample crystallizing, however, with tetragonal symmetry. Hence, most likely, the significantly higher Li conductivity previously reported for a cubic LLZ sample cannot be ascribed solely to the slight structural distortions accompanying the change of the crystal symmetry. Here, even Al impurities, acting as stabilizer for the cubic polymorph at room temperature, do not lead to the high ion conductivity reported previously. © by Oldenbourg Wissenschaftsverlag, München.