diff --git a/pkgs/servers/mail/mailman/python.nix b/pkgs/servers/mail/mailman/python.nix
index e107bd0bcea8..dc7601afa8da 100644
--- a/pkgs/servers/mail/mailman/python.nix
+++ b/pkgs/servers/mail/mailman/python.nix
@@ -24,7 +24,7 @@ lib.fix (self: python3.override {
       hiredis = super.hiredis.overrideAttrs (new: { src, ... }: {
         version = "3.1.0";
         src = src.override {
-          rev = "refs/tags/v${new.version}";
+          tag = new.version;
           hash = "sha256-ID5OJdARd2N2GYEpcYOpxenpZlhWnWr5fAClAgqEgGg=";
         };
       });