  It is well known that the tri-bimaximal neutrino mixing pattern V_0 can be
derived from a class of flavor models with the non-Abelian A_4 symmetry. We
point out that small corrections to V_0, which are inherent in the A_4 models
and arise from both the charged-lepton and neutrino sectors, have been omitted
in the previous works. We show that such corrections may lead the 3 \times 3
neutrino mixing matrix V to a non-unitary deviation from V_0, but they cannot
result in a nonzero value of \theta_13 or any new CP-violating phases. Current
experimental constraints on the unitarity of V allow us to constrain the model
parameters to some extent.
