In this Note, we apply Koebke's equivalence theory to a uniform slab lattice of symmetric cells on which a macroscopic buckling is superimposed. It is shown that Koebke's procedure, up to second-order accuracy in buckling, leads to Benoist's (corrected) definition of diffusion coefficient, and the discontinuity factors are found to be independent of the position of the cell in the lattice. Some comments regarding the use of equivalence theory in typical reactor core calculations are also made.