The tracer diffusion coefficient of In-111 has been investigated in the chalcopyrite CuInS2 at 650 degrees C for different sulfur partial pressures p(s2). The unusual shape of the profiles are attributed to two different volume diffusion processes of indium in the compound giving rise to two diffusion coefficients D-1* and D-2*. The observed decrease of the tracer diffusion coefficients with increasing P-s2 is discussed in respect to the point defect structure of CuInS2 and the migration mechanisms of cations in the chalcopyrite structure.