[en] X-ray powder diffraction and differential thermal analysis (DTA) measurements were made on polycrystalline samples of the Cu₂Zn_1-zFe_zGeSe₄ alloy system. The diffraction patterns were used to show the equilibrium conditions and to estimate crystalline parameter values. It was found that, at room temperature, a single phase solid solution with the tetragonal stannite α structure (I4-bar2m) occurs across the whole composition range. The DTA thermograms were used to construct the phase diagram of the Cu₂Zn_1-zFe_zGeSe₄ alloy system. It was confirmed that the Cu₂ZnGeSe₄ compound melts incongruently. It was observed that undercooling effects occur for samples with z > 0.9