inets-4.7.6/src/http_util.erl contains this code: integer_to_hexlist(Num)-> integer_to_hexlist(Num, get_size(Num), []). Which should probably be: integer_to_hexlist(Num) when integer(Num) -> integer_to_hexlist(Num, get_size(Num), []). Thank you, Julian ps. do not do this: http_util:integer_to_hexlist([0]).