It is shown that the famous Allen–Dynes asymtotic limit for superconducting transition temperature in very strong coupling region (Formula presented.) (where λ ≫ 1 is Eliashberg–McMillan electron–phonon coupling constant and Ω0 – the characteristic frequency of phonons) in antiadiabatic limit of Eliashberg equations Ω0/D ≫ 1 (D ~ EF is conduction band half-width and EF is Fermi energy) is replaced by (Formula presented.) with the upper limit for Tc given by (Formula presented.).