diff --git a/test/lisp/gnus/mml-sec-tests.el b/test/lisp/gnus/mml-sec-tests.el
index 8f78a66f616..272918688d8 100644
--- a/test/lisp/gnus/mml-sec-tests.el
+++ b/test/lisp/gnus/mml-sec-tests.el
@@ -663,6 +663,7 @@ In this test, just multiple encryption and signing keys may be available."
 (ert-deftest mml-secure-en-decrypt-sign-1-3-double ()
   "Sign and encrypt message; then decrypt and test for expected result.
 In this test, just multiple encryption and signing keys may be available."
+  :tags '(:unstable)
   (skip-unless (test-conf))
   (mml-secure-test-key-fixture
    (lambda ()
@@ -714,6 +715,7 @@ In this test, lists of encryption and signing keys are customized."
 (ert-deftest mml-secure-en-decrypt-sign-3 ()
   "Sign and encrypt message; then decrypt and test for expected result.
 Use sign-with-sender and encrypt-to-self."
+  :tags '(:unstable)
   (skip-unless (test-conf))
   (mml-secure-test-key-fixture
    (lambda ()