rails don't supoort mysql bigint?

hi

rails 1.2.6 mysql 5

table:infos
fields:id ,bigint(20), AUTO_INCREMENT =90000000013
        name,varchar(255)

info_controllor.rb
def add
      @info = Info.new
      @info.name = "ddd111"
      @info.save!
      puts "id:",@info.id.to_s
end

run...
    id:-194313203

why?rails don't supoort mysql bigint?

thx~~~