diff --git a/src/calibre/utils/formatter_functions.py b/src/calibre/utils/formatter_functions.py
index 6b79e23b5e..92ebe72706 100644
--- a/src/calibre/utils/formatter_functions.py
+++ b/src/calibre/utils/formatter_functions.py
@@ -460,6 +460,7 @@ class UserFunction(FormatterUserFunction):
     return cls
 
 def load_user_template_functions(funcs):
+    formatter_functions.reset_to_builtins()
     for func in funcs:
         try:
             cls = compile_user_function(*func)