  Generally the diagonalization of the mass matrix of the charged leptons is a
part of the neutrino UPMNS matrix. However, usually this contribution is
ignored by assuming a diagonal mass matrix for charged leptons. In this letter
we test this common assumption in the context of neutrino physics. Our
analytical and numerical results for two supersymmetric models reveal that such
a simplification is not justified. Especially for the solar and reactor mixing
angles important modifications are found.
