The proof of Theorem 6 in the paper by J. He and X. Yao [Artificial Intelligence 127 (1) (2001) 57-85] contains a mistake, although the theorem is correct [S. Droste et al., Theoret. Comput. Sci. 276 (2002) 51-81]. This note gives a revised proof and theorem. It turns out that the revised theorem is more general than the original one given an evolutionary algorithm with mutation probability p(m) = 1/(2n), using the same proof method as given by J. He and X. Yao [Artificial Intelligence 127 (1) (2001) 57-85]. (C) 2002 Elsevier Science B.V. All rights reserved.