diff --git a/src/calibre/utils/formatter_functions.py b/src/calibre/utils/formatter_functions.py
index 7077d4a468..3141534838 100644
--- a/src/calibre/utils/formatter_functions.py
+++ b/src/calibre/utils/formatter_functions.py
@@ -1634,6 +1634,7 @@ class BuiltinCheckYesNo(BuiltinFormatterFunction):
             return 'yes'
         return ""
 
+
 class BuiltinRatingToStars(BuiltinFormatterFunction):
     name = 'rating_to_stars'
     arg_count = 2
@@ -1657,6 +1658,7 @@ class BuiltinRatingToStars(BuiltinFormatterFunction):
         from calibre.ebooks.metadata import rating_to_stars
         return rating_to_stars(v, use_half_stars == '1')
 
+
 _formatter_builtins = [
     BuiltinAdd(), BuiltinAnd(), BuiltinApproximateFormats(), BuiltinAssign(),
     BuiltinAuthorLinks(), BuiltinAuthorSorts(), BuiltinBooksize(),