Here is my code:

external_encoding = Encoding::SJIS
html = open(file, "r:#{external_encoding}", invalid: :replace, undef: :replace ) do |f|
require "nkf"
external_encoding = NKF.guess(f.read)
f.reopen(file, "r:#{external_encoding}")
f.read
end

Exception

My file is a Japanese file.So NKF.guess's value is ISO-2022-JP.
But Exception throws in f.reopen :

ArgumentError:ASCII incompatible encoding needs binmode when using NKF

Environment

jruby-9.1.8.0
Windows7_X64