diff --git a/src/calibre/ebooks/lit/writer.py b/src/calibre/ebooks/lit/writer.py
index 86d10965a4..1e72ab2e4a 100644
--- a/src/calibre/ebooks/lit/writer.py
+++ b/src/calibre/ebooks/lit/writer.py
@@ -300,7 +300,7 @@ class LitWriter(object):
         oeb.metadata.add('calibre-version', calibre.__version__)
         cover = None
         if oeb.metadata.cover:
-            id = str(oeb.metadata.cover[0])
+            id = unicode(oeb.metadata.cover[0])
             cover = oeb.manifest.ids[id]
             for type, title in ALL_MS_COVER_TYPES:
                 if type not in oeb.guide:
diff --git a/src/calibre/ebooks/oeb/reader.py b/src/calibre/ebooks/oeb/reader.py
index 02b3b92b01..09807ea636 100644
--- a/src/calibre/ebooks/oeb/reader.py
+++ b/src/calibre/ebooks/oeb/reader.py
@@ -530,7 +530,7 @@ class OEBReader(object):
 
     def _locate_cover_image(self):
         if self.oeb.metadata.cover:
-            id = str(self.oeb.metadata.cover[0])
+            id = unicode(self.oeb.metadata.cover[0])
             item = self.oeb.manifest.ids.get(id, None)
             if item is not None and item.media_type in OEB_IMAGES:
                 return item