diff --git a/tests/sys/kern/Makefile b/tests/sys/kern/Makefile
--- a/tests/sys/kern/Makefile
+++ b/tests/sys/kern/Makefile
@@ -27,6 +27,9 @@
 ATF_TESTS_C+=	reaper
 ATF_TESTS_C+=	sched_affinity
 ATF_TESTS_C+=	sigaltstack
+ATF_TESTS_C+=	sigsys
+TEST_METADATA.sigsys+=	is_exclusive="true"
+TEST_METADATA.sigsys+=	required_user="root"
 ATF_TESTS_C+=	sigwait
 ATF_TESTS_C+=	socket_accf
 ATF_TESTS_C+=	socket_msg_trunc
diff --git a/tests/sys/kern/sigsys.c b/tests/sys/kern/sigsys.c
new file mode 100644
--- /dev/null
+++ b/tests/sys/kern/sigsys.c
@@ -0,0 +1,122 @@
+/*-
+ * Copyright (c) 2023 Dmitry Chagin <dchagin@FreeBSD.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <sys/syscall.h>
+#include <sys/sysctl.h>
+
+#include <atf-c.h>
+#include <errno.h>
+#include <signal.h>
+
+static volatile sig_atomic_t signals = 0;
+static volatile sig_atomic_t signo = 0;
+
+static void
+handler(int sig)
+{
+
+	signo = sig;
+	signals++;
+}
+
+static void
+sysctlset(const char *name, int32_t val)
+{
+
+	ATF_REQUIRE(sysctlbyname(name, NULL, NULL, &val, sizeof(val)) == 0);
+}
+
+static void
+test_sigsys(bool sigsys)
+{
+	int error;
+
+	ATF_REQUIRE(signal(SIGSYS, handler) != SIG_ERR);
+
+	/* 11 - obsolete execv */
+	signals = signo = 0;
+	error = syscall(11, 0, 1);
+	ATF_REQUIRE(error == -1);
+	ATF_REQUIRE(errno == ENOSYS);
+	if (sigsys) {
+		ATF_REQUIRE(signals == 1);
+		ATF_REQUIRE(signo == SIGSYS);
+	} else
+		ATF_REQUIRE(signals == 0);
+	/* loadable syscall */
+	signals = signo = 0;
+	error = syscall(SYS_nfssvc, 0, 1);
+	ATF_REQUIRE(error == -1);
+	ATF_REQUIRE(errno == ENOSYS || errno == EINVAL);
+	if (sigsys) {
+		ATF_REQUIRE(signals == 0 || signals == 1);
+		ATF_REQUIRE(signo == SIGSYS || signo == 0);
+	} else
+		ATF_REQUIRE(signals == 0);
+	/* non-existent syscall */
+	signals = signo = 0;
+	error = syscall(SYS_MAXSYSCALL + 1, 0, 1);
+	ATF_REQUIRE(error == -1);
+	ATF_REQUIRE(errno == ENOSYS);
+	if (sigsys) {
+		ATF_REQUIRE(signals == 1);
+		ATF_REQUIRE(signo == SIGSYS);
+	} else
+		ATF_REQUIRE(signals == 0);
+}
+
+/* Test SIGSYS with knob kern.signosys=1 */
+ATF_TC_WITH_CLEANUP(test_sigsys_on);
+ATF_TC_HEAD(test_sigsys_on, tc)
+{
+
+	atf_tc_set_md_var(tc, "require.user", "root");
+	atf_tc_set_md_var(tc, "descr", "Test SIGSYS with kern.signosys on");
+}
+
+ATF_TC_BODY(test_sigsys_on, tc)
+{
+
+	sysctlset("kern.signosys", 1);
+	test_sigsys(true);
+}
+
+ATF_TC_CLEANUP(test_sigsys_on, tc)
+{
+
+	sysctlset("kern.signosys", 1);
+}
+
+/* Test SIGSYS with knob kern.signosys=0 */
+ATF_TC_WITH_CLEANUP(test_sigsys_off);
+ATF_TC_HEAD(test_sigsys_off, tc)
+{
+
+	atf_tc_set_md_var(tc, "require.user", "root");
+	atf_tc_set_md_var(tc, "descr", "Test SIGSYS with kern.signosys off");
+}
+
+ATF_TC_BODY(test_sigsys_off, tc)
+{
+
+	sysctlset("kern.signosys", 0);
+	test_sigsys(false);
+}
+
+ATF_TC_CLEANUP(test_sigsys_off, tc)
+{
+
+	sysctlset("kern.signosys", 1);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+
+	ATF_TP_ADD_TC(tp, test_sigsys_on);
+	ATF_TP_ADD_TC(tp, test_sigsys_off);
+
+	return (atf_no_error());
+}