Using nokogiri to validate xml: finding the line-nr of validation errors?

I am trying to validate pretty large xml-files against a xsd-schema. Nokogiri does this perfectly fine, using the following code:

  xsd = Nokogiri::XML::Schema(File.read('batch_schema.xsd'))
  doc = Nokogiri::XML(File.read('batch205.xml'))

  xsd.validate(doc).each do |error|
    puts "#{error.line} :: #{error.message}"
  end

Simple enough. Only: error.line is always 65535. Because the xml files we need to check are really huge, it would be really-really helpful to get the line-numbers.

I found this cheatsheet so that is where I found the option to read the line.

In the libxml2 documentation I found you have to enable line-numbers for it to be set. Any idea how to enable line-numbers with nokogiri or get a line-number in a validation-error?