diff --git a/lib/oauth.js b/lib/oauth.js
index e407180..8ee56ce 100644
--- a/lib/oauth.js
+++ b/lib/oauth.js
@@ -325,7 +325,7 @@ exports.OAuth.prototype._performSecureRequest= function( oauth_token, oauth_toke
     post_body= querystring.stringify(extra_params);
   }
 
-  headers["Content-length"]= post_body ? post_body.length : 0; //Probably going to fail if not posting ascii
+  headers["Content-length"]= post_body ? Buffer.byteLength(post_body) : 0;
   headers["Content-Type"]= post_content_type;
    
   var path;