diff --git a/tests/external.nix b/tests/external.nix
index 7579b6d..c7e9a0d 100644
--- a/tests/external.nix
+++ b/tests/external.nix
@@ -402,7 +402,7 @@ pkgs.nixosTest {
           client.succeed("fetchmail  --nosslcertck -v")
           client.succeed("cat ~/mail/* >&2")
           # make sure it is dkim signed
-          client.succeed("grep DKIM ~/mail/*")
+          client.succeed("grep DKIM-Signature: ~/mail/*")
 
       with subtest("aliases"):
           client.execute("rm ~/mail/*")