diff --git a/src/calibre/ebooks/metadata/book/json_codec.py b/src/calibre/ebooks/metadata/book/json_codec.py
index fc95749f12..7435a9387b 100644
--- a/src/calibre/ebooks/metadata/book/json_codec.py
+++ b/src/calibre/ebooks/metadata/book/json_codec.py
@@ -149,7 +149,7 @@ class JsonCodec(object):
         value = book.get(key)
         if key == 'thumbnail':
             return encode_thumbnail(value)
-        elif isbytestring(value): # str includes bytes
+        elif isbytestring(value):  # str includes bytes
             enc = filesystem_encoding if key == 'lpath' else preferred_encoding
             return object_to_unicode(value, enc=enc)
         elif datatype == 'datetime':