diff --git a/src/calibre/ebooks/metadata/book/__init__.py b/src/calibre/ebooks/metadata/book/__init__.py
index b7ab91c26f..00bbc68f29 100644
--- a/src/calibre/ebooks/metadata/book/__init__.py
+++ b/src/calibre/ebooks/metadata/book/__init__.py
@@ -135,5 +135,4 @@ SERIALIZABLE_FIELDS =      SOCIAL_METADATA_FIELDS.union(
 # A special set used to optimize the performance of Metadata.__setattr__
 ATTR_NORMAL_FIELDS =    frozenset(STANDARD_METADATA_FIELDS -
                                      TOP_LEVEL_IDENTIFIERS -
-                                     set('identifiers') -
-                                     set('languages'))
+                                     set('identifiers'))