From 7020ce507edcf494d141697a1734081e6994c69b Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sun, 17 Oct 2010 08:14:12 -0600
Subject: [PATCH] Fix #7198 (EPUB issue- Incorrect format for language in
 toc.ncx)

---
 src/calibre/ebooks/oeb/base.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py
index e85098e293..2d2945c26a 100644
--- a/src/calibre/ebooks/oeb/base.py
+++ b/src/calibre/ebooks/oeb/base.py
@@ -1908,6 +1908,7 @@ class OEBBook(object):
 
     def _to_ncx(self):
         lang = unicode(self.metadata.language[0])
+        lang = lang.replace('_', '-')
         ncx = etree.Element(NCX('ncx'),
             attrib={'version': '2005-1', XML('lang'): lang},
             nsmap={None: NCX_NS})