diff --git a/nixos/tests/sympa.nix b/nixos/tests/sympa.nix
index 280691f7cb4..eb38df180a7 100644
--- a/nixos/tests/sympa.nix
+++ b/nixos/tests/sympa.nix
@@ -30,7 +30,7 @@ import ./make-test-python.nix ({ pkgs, lib, ... }: {
     machine.wait_for_unit("sympa.service")
     machine.wait_for_unit("wwsympa.service")
     assert "Mailing lists service" in machine.succeed(
-        "curl --insecure -L http://localhost/"
+        "curl --fail --insecure -L http://localhost/"
     )
   '';
 })