diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 843e6ca450..af0639ed4b 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -427,7 +427,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
 
         custom_map = self.custom_columns_in_meta()
         # custom col labels are numbers (the id in the custom_columns table)
-        custom_cols = list(sorted(custom_map.keys()))
+        custom_cols = sorted(custom_map.keys())
         lines.extend([custom_map[x] for x in custom_cols])
 
         self.FIELD_MAP = {'id':0, 'title':1, 'authors':2, 'timestamp':3,