diff --git a/src/calibre/ebooks/metadata/book/serialize.py b/src/calibre/ebooks/metadata/book/serialize.py
index 8f7f46fa4a..7fc54f1eed 100644
--- a/src/calibre/ebooks/metadata/book/serialize.py
+++ b/src/calibre/ebooks/metadata/book/serialize.py
@@ -26,7 +26,7 @@ def ensure_unicode(obj, enc=preferred_encoding):
 
 def read_cover(mi):
     if mi.cover_data and mi.cover_data[1]:
-        return
+        return mi
     if mi.cover:
         try:
             with lopen(mi.cover, 'rb') as f: