diff --git a/src/tests/unittests/Makefile.am b/src/tests/unittests/Makefile.am
index b6bef298..8708e464 100644
--- a/src/tests/unittests/Makefile.am
+++ b/src/tests/unittests/Makefile.am
@@ -32,6 +32,14 @@ compression_SOURCES = compression.c
 compression_LDADD = $(LDADD) $(OPTIONAL_ZLIB_LIBS)
 endif
 
+if ENABLE_OPENSSL
+noinst_PROGRAMS += sm
+TESTS += sm
+
+sm_SOURCES = sm.c
+sm_LDADD = $(top_builddir)/src/sm/libsm.la $(LDADD)
+endif
+
 
 
 endif
diff --git a/src/tests/unittests/sm.c b/src/tests/unittests/sm.c
new file mode 100644
index 00000000..75cce97d
--- /dev/null
+++ b/src/tests/unittests/sm.c
@@ -0,0 +1,69 @@
+/*
+ * sm.c: Unit tests for Secure Messaging
+ *
+ * Copyright (C) 2021 Red Hat, Inc.
+ *
+ * Author: Jakub Jelen <jjelen@redhat.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "torture.h"
+#include "libopensc/log.c"
+#include "sm/sm-common.h"
+
+static void torture_sm_incr_ssc(void **state)
+{
+	unsigned char in[] = {0x00, 0x00};
+
+	(void)state;
+
+	/* just make sure it does not crash */
+	sm_incr_ssc(NULL, 0);
+
+	/* zero-length input should not underflow the buffer */
+	sm_incr_ssc(in, 0);
+
+	/* shortest possible input */
+	in[0] = 0x42;
+	sm_incr_ssc(in, 1);
+	assert_int_equal(in[0], 0x43);
+
+	/* overflow to the second byte */
+	in[0] = 0x00;
+	in[1] = 0xff;
+	sm_incr_ssc(in, 2);
+	assert_int_equal(in[0], 0x01);
+	assert_int_equal(in[1], 0x00);
+
+	/* overflow */
+	in[0] = 0xff;
+	in[1] = 0xff;
+	sm_incr_ssc(in, 2);
+	assert_int_equal(in[0], 0x00);
+	assert_int_equal(in[1], 0x00);
+}
+
+
+int main(void)
+{
+	int rc;
+	struct CMUnitTest tests[] = {
+		/* sm_incr_ssc */
+		cmocka_unit_test(torture_sm_incr_ssc),
+	};
+
+	rc = cmocka_run_group_tests(tests, NULL, NULL);
+	return rc;
+}