diff --git a/src/calibre/ebooks/lit/oeb.py b/src/calibre/ebooks/lit/oeb.py
index 42b54561d1..bc705f9c64 100644
--- a/src/calibre/ebooks/lit/oeb.py
+++ b/src/calibre/ebooks/lit/oeb.py
@@ -346,7 +346,7 @@ class Manifest(object):
 
     def to_opf1(self, parent=None):
         elem = element(parent, 'manifest')
-        for item in self.items.values():
+        for item in self.ids.values():
             media_type = item.media_type
             if media_type == XHTML_MIME:
                 media_type = OEB_DOC_MIME