diff --git a/pkgs/servers/mail/mailman/hyperkitty.nix b/pkgs/servers/mail/mailman/hyperkitty.nix
index 00cf2c1e83c0..054d9dcf91a0 100644
--- a/pkgs/servers/mail/mailman/hyperkitty.nix
+++ b/pkgs/servers/mail/mailman/hyperkitty.nix
@@ -7,6 +7,8 @@
 
 buildPythonPackage rec {
   pname = "HyperKitty";
+  # Note: Mailman core must be on the latest version before upgrading HyperKitty.
+  # See: https://gitlab.com/mailman/postorius/-/issues/516#note_544571309
   version = "1.3.3";
   disabled = !isPy3k;
 
diff --git a/pkgs/servers/mail/mailman/postorius.nix b/pkgs/servers/mail/mailman/postorius.nix
index fc9f6217d934..189e152fce03 100644
--- a/pkgs/servers/mail/mailman/postorius.nix
+++ b/pkgs/servers/mail/mailman/postorius.nix
@@ -4,6 +4,8 @@
 
 buildPythonPackage rec {
   pname = "postorius";
+  # Note: Mailman core must be on the latest version before upgrading Postorious.
+  # See: https://gitlab.com/mailman/postorius/-/issues/516#note_544571309
   version = "1.3.4";
 
   src = fetchPypi {