diff --git a/src/calibre/db/categories.py b/src/calibre/db/categories.py
index d169e5a5c4..1b57fe8e0a 100644
--- a/src/calibre/db/categories.py
+++ b/src/calibre/db/categories.py
@@ -14,7 +14,7 @@ from calibre.library.field_metadata import TagsIcons
 from calibre.utils.config_base import tweaks
 from calibre.utils.icu import sort_key
 
-CATEGORY_SORTS = { 'name', 'popularity', 'rating' }
+CATEGORY_SORTS = ('name', 'popularity', 'rating') # This has to be a tuple not a set
 
 class Tag(object):
 
diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 5149b7a0de..d93833ae9c 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -44,7 +44,7 @@ from calibre.utils.recycle_bin import delete_file, delete_tree
 from calibre.utils.formatter_functions import load_user_template_functions
 from calibre.db.errors import NoSuchFormat
 from calibre.db.lazy import FormatMetadata, FormatsList
-from calibre.db.categories import Tag
+from calibre.db.categories import Tag, CATEGORY_SORTS
 from calibre.utils.localization import (canonicalize_lang,
         calibre_langcode_to_name)
 
@@ -1644,7 +1644,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
 
 ########## data structures for get_categories
 
-    CATEGORY_SORTS = ('name', 'popularity', 'rating')
+    CATEGORY_SORTS = CATEGORY_SORTS
     MATCH_TYPE = ('any', 'all')
 
     class TCat_Tag(object):