diff --git a/nixos/modules/services/mail/mailman.nix b/nixos/modules/services/mail/mailman.nix
index 326052731a31a..e3c014a6c6557 100644
--- a/nixos/modules/services/mail/mailman.nix
+++ b/nixos/modules/services/mail/mailman.nix
@@ -595,6 +595,7 @@ in {
             plugins = ["python3"];
             home = webEnv;
             http = "127.0.0.1:18507";
+            buffer-size = 8192;
           }
           // (if cfg.serve.virtualRoot == "/"
             then { module = "mailman_web.wsgi:application"; }