  Let f_t be a meromorphic family of endomorphisms of P^N_C of degree at least
2, and let L(f_t) be the sum of Lyapunov exponents associated to f_t. Favre
showed that L(f_t)=L(f)\log|t^{-1}|+o(\log|t^{-1}|) as t -> 0, where L(f) is
the sum of Lyapunov exponents on the generic fibre, interpreted as an
endomorphism of some projective Berkovich space. Under some additional
constraints on the family, we provide an explicit error term.
