diff --git a/docs/releases/4.2.21.txt b/docs/releases/4.2.21.txt
index cd1d26d779..fa59deff06 100644
--- a/docs/releases/4.2.21.txt
+++ b/docs/releases/4.2.21.txt
@@ -7,6 +7,11 @@ Django 4.2.21 release notes
 Django 4.2.21 fixes a security issue with severity "moderate", a data loss bug,
 and a regression in 4.2.20.
 
+This release was built using an upgraded :pypi:`setuptools`, producing
+filenames compliant with :pep:`491` and :pep:`625` and thus addressing a PyPI
+warning about non-compliant distribution filenames. This change only affects
+the Django packaging process and does not impact Django's behavior.
+
 CVE-2025-32873: Denial-of-service possibility in ``strip_tags()``
 =================================================================