Perturbed angular correlation measurements in Indium implanted GaN and AlN have shown that after annealing up to 50% of the In probes occupy relatively undisturbed substitutional group III sites at 293 K while the remaining fraction traps a nearest neighbor point defect. Above 293 K this fraction decreases strongly until, at 1100 K, all In probes are found in undisturbed substitutional sites. The effect is completely reversible. A model involving an Indium–nitrogen vacancy complex is suggested to explain this behavior. Possibly this complex can act as radiative recombination center or as seed for phase segregation during growth.