diff --git a/tests/client/torture_auth.c b/tests/client/torture_auth.c
index d3e71d9e..fa58c14a 100644
--- a/tests/client/torture_auth.c
+++ b/tests/client/torture_auth.c
@@ -296,9 +296,21 @@ static void torture_auth_pubkey(void **state) {
     rc = ssh_pki_import_privkey_file(bob_ssh_key, NULL, NULL, NULL, &privkey);
     assert_int_equal(rc, SSH_OK);
 
+    /* negative tests */
+    rc = ssh_userauth_try_publickey(NULL, NULL, privkey);
+    assert_int_equal(rc, SSH_AUTH_ERROR);
+    rc = ssh_userauth_try_publickey(session, NULL, NULL);
+    assert_int_equal(rc, SSH_AUTH_ERROR);
+
     rc = ssh_userauth_try_publickey(session, NULL, privkey);
     assert_int_equal(rc, SSH_AUTH_SUCCESS);
 
+    /* negative tests */
+    rc = ssh_userauth_publickey(NULL, NULL, privkey);
+    assert_int_equal(rc, SSH_AUTH_ERROR);
+    rc = ssh_userauth_publickey(session, NULL, NULL);
+    assert_int_equal(rc, SSH_AUTH_ERROR);
+
     rc = ssh_userauth_publickey(session, NULL, privkey);
     assert_int_equal(rc, SSH_AUTH_SUCCESS);
 
diff --git a/tests/client/torture_auth_common.c b/tests/client/torture_auth_common.c
index 15e407ab..8a4f2854 100644
--- a/tests/client/torture_auth_common.c
+++ b/tests/client/torture_auth_common.c
@@ -52,6 +52,10 @@ void torture_auth_agent(void **state)
     rc = ssh_userauth_list(session, NULL);
     assert_true(rc & SSH_AUTH_METHOD_PUBLICKEY);
 
+    /* negative test case */
+    rc = ssh_userauth_agent(NULL, NULL);
+    assert_int_equal(rc, SSH_AUTH_ERROR);
+
     rc = ssh_userauth_agent(session, NULL);
     assert_ssh_return_code(session, rc);
 }