diff --git a/unit/test-wsc.c b/unit/test-wsc.c
index c26a109c..66e03e01 100644
--- a/unit/test-wsc.c
+++ b/unit/test-wsc.c
@@ -1166,6 +1166,22 @@ static void wsc_test_parse_m4(const void *data)
 					encrypted.iov_base, encrypted.iov_len));
 }
 
+static void wsc_test_build_m4(const void *data)
+{
+	const struct m4_data *test = data;
+	uint8_t *out;
+	size_t out_len;
+
+	out = wsc_build_m4(&test->expected, test->expected_encrypted,
+				test->expected_encrypted_size, &out_len);
+	assert(out);
+
+	assert(out_len == test->len);
+	assert(!memcmp(test->pdu, out, test->len));
+
+	l_free(out);
+}
+
 int main(int argc, char *argv[])
 {
 	l_test_init(&argc, &argv);
@@ -1209,6 +1225,7 @@ int main(int argc, char *argv[])
 	l_test_add("/wsc/build/m3 1", wsc_test_build_m3, &m3_data_1);
 
 	l_test_add("/wsc/parse/m4 1", wsc_test_parse_m4, &m4_data_1);
+	l_test_add("/wsc/build/m4 1", wsc_test_build_m4, &m4_data_1);
 
 	return l_test_run();
 }