Problem with private_class_method using JRuby

private_class_method_test.rb

require 'ffi'

module Sys
  class Filesystem
    extend FFI::Library
    ffi_lib FFI::Library::LIBC

    if RbConfig::CONFIG['host_os'] =~ /darwin|osx|mach/i
      attach_function(:getmntinfo, :getmntinfo64, [:pointer, :int], :int)
    else
      attach_function(:getmntinfo, [:pointer, :int], :int)
    end

    # This seems to be the problem for JRuby
    private_class_method :getmntinfo

    def self.mounts
      if method_defined?(:getmntinfo)
        puts "YEP"
      else
        puts "NOPE"
      end
    end
  end
end

# MRI returns "YEP", JRuby returns "NOPE"
Sys::Filesystem.mounts