diff --git a/nixos/tests/custom-ca.nix b/nixos/tests/custom-ca.nix
index 67f7b3ff1f1..31909188d3a 100644
--- a/nixos/tests/custom-ca.nix
+++ b/nixos/tests/custom-ca.nix
@@ -92,13 +92,19 @@ in
         { onlySSL = true;
           sslCertificate = "${example-good-cert}/server.crt";
           sslCertificateKey = "${example-good-cert}/server.key";
-          locations."/".extraConfig = "return 200 'It works!';";
+          locations."/".extraConfig = ''
+            add_header Content-Type text/plain;
+            return 200 'It works!';
+          '';
         };
       services.nginx.virtualHosts."bad.example.com" =
         { onlySSL = true;
           sslCertificate = "${example-bad-cert}/server.crt";
           sslCertificateKey = "${example-bad-cert}/server.key";
-          locations."/".extraConfig = "return 200 'It does not work!';";
+          locations."/".extraConfig = ''
+            add_header Content-Type text/plain;
+            return 200 'It does not work!';
+          '';
         };
 
       environment.systemPackages = with pkgs;