Perturbed angular correlation measurements in the HfAl 2 C14-type Laves phase exhibit a very surprising temperature behavior of the ion-implanted 1 1 1 In probe atoms. Below 370<space>K the 1 1 1 In impurities are located at the unique hafnium site. Above 400 K they occupy the two aluminum sites, however with a clear preference of the 2(a) site. This process, which is fully reversible when heating and cooling the sample, is attributed to atomic size effects.