Abstract. Let a sequence Λ ⊂ C be such that the corresponding system of exponential functions E(Λ) := {e iλt } λ∈Λ is complete and minimal in L 2 (−π, π) and thus each function f ∈ L 2 (−π, π) corresponds to a non-harmonic Fourier series in E(Λ). We prove that if the generating function G of Λ satisfies Muckenhoupt (A 2 ) condition on R, then this series admits a linear summation method. Recent results show that (A 2 ) condition cannot be omitted.