diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index acd5442..6119bee 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -875,6 +875,10 @@
 
    .. versionadded:: 3.3
 
+   .. note::
+
+      The addition of new required attributes must go through the normal PEP
+      process. See :pep:`421` for more information.
 
 .. data:: int_info