The structures of SmAlSi and SmAlGe were determined by the powder diffraction method. These compounds have a tetragonal structure of LaPtSi type, which is a ternary substitutional variant of α-ThSi2. Both prototype structures have the same extinction rules, and as a result, the choice of the structural type must be based on very careful examination of the peak intensities. This was done with the aid of a Rietveld refinement, which indicates a better fit of the LaPtSi structure.