diff --git a/src/calibre/db/cli/cmd_list.py b/src/calibre/db/cli/cmd_list.py
index d28b1dae24..0b9395d635 100644
--- a/src/calibre/db/cli/cmd_list.py
+++ b/src/calibre/db/cli/cmd_list.py
@@ -284,7 +284,11 @@ List the books available in the calibre database.
         '--sort-by',
         default=None,
         help=_(
-            'The field by which to sort the results. You can specify multiple fields by separating them with commas.\nAvailable fields: {0}\nDefault: {1}'
+            'The field by which to sort the results. You can specify multiple fields by'
+            ' separating them with commas.\nAvailable fields: {0}\nDefault: {1}.'
+            ' In addition to the builtin fields above, custom fields are'
+            ' also available as *field_name, for example, for a custom field'
+            ' #rating, use the name: *rating'
         ).format(', '.join(sorted(FIELDS)), 'id')
     )
     parser.add_option(