HTTParty and text/xml

I'm trying to make a POST request using HTTParty, in which I need the content-type to be text/xml. How can I make that happen? Right now the API I'm calling is 开发者_如何学Pythoncomplaining I'm not sending any xml. If I call it using curl I get the same error, unless I specify content-type to text/xml.

HTTParty.post url, :body => xml, :headers => {'Content-type' => 'text/xml'}