diff --git a/src/calibre/ebooks/oeb/base.py b/src/calibre/ebooks/oeb/base.py index 8934a4d174..b798c0fc13 100644 --- a/src/calibre/ebooks/oeb/base.py +++ b/src/calibre/ebooks/oeb/base.py @@ -1903,7 +1903,10 @@ class OEBBook: return def _to_ncx(self): - lang = str(self.metadata.language[0]) + try: + lang = str(self.metadata.language[0]) + except IndexError: + lang = 'en' lang = lang.replace('_', '-') ncx = etree.Element(NCX('ncx'), attrib={'version': '2005-1', XML('lang'): lang},