The concentration dependence of the mutual diffusion coefficients in the ternary liquid mixture glycerol + acetone + water is determined at 298.15 K by the Taylor dispersion technique along two concentration paths of constant water mole fractions of 0.468 and 0.420, ranging from the binary subsystem toward the phase boundary in the vicinity of the critical solution point. The eigenvalues of Fick's diffusion coefficient matrix are given, and the influence of the optical properties of the system on the diffusion coefficient determination is discussed. It was found that the determinant vertical bar D vertical bar continuously declines on approaching the phase boundary.