  Weak interaction contributions to the strong theta parameter are revisited in
the frame of a large-Nc Chiral Perturbation Theory. Focusing on the hadronic
(eta,etaprime) \to pi pi amplitudes, we express these second-order corrections
in terms of the CP-violating parameter in K \to pi pi decays to obtain
Delta_w(theta) approx 10^{-17} at O(GF^2 epsilonprime).
