diff --git a/tests/generator/not_impl_header.txt b/tests/generator/not_impl_header.txt
index cd6f8f5a1..4ceefff4d 100644
--- a/tests/generator/not_impl_header.txt
+++ b/tests/generator/not_impl_header.txt
@@ -1,2 +1,7 @@
+# WARNING: THIS IS AN AUTOMATICALLY GENERATED FILE
+# EDIT tests/not_impl_gen.py, NOT THIS FILE.
+# RESULTS OF THIS TEST DEPEND ON THE CPYTHON
+# VERSION USED TO RUN not_impl_gen.py
+
 import platform