diff --git a/sys/amd64/amd64/elf_machdep.c b/sys/amd64/amd64/elf_machdep.c
--- a/sys/amd64/amd64/elf_machdep.c
+++ b/sys/amd64/amd64/elf_machdep.c
@@ -80,7 +80,8 @@
 	.sv_fixlimit	= NULL,
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_ABI_FREEBSD | SV_ASLR | SV_LP64 | SV_SHP |
-			    SV_TIMEKEEP | SV_RNG_SEED_VER | SV_DSO_SIG,
+			    SV_TIMEKEEP | SV_RNG_SEED_VER | SV_DSO_SIG |
+			    SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
@@ -122,7 +123,8 @@
 	.sv_fixlimit	= NULL,
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_ABI_FREEBSD | SV_ASLR | SV_LP64 | SV_SHP |
-			    SV_TIMEKEEP | SV_RNG_SEED_VER | SV_DSO_SIG,
+			    SV_TIMEKEEP | SV_RNG_SEED_VER | SV_DSO_SIG |
+			    SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c
--- a/sys/amd64/amd64/trap.c
+++ b/sys/amd64/amd64/trap.c
@@ -1032,10 +1032,10 @@
 		regcnt--;
 	}
 
- 	if (sa->code >= p->p_sysent->sv_size)
- 		sa->callp = &p->p_sysent->sv_table[0];
-  	else
- 		sa->callp = &p->p_sysent->sv_table[sa->code];
+	if (sa->code >= p->p_sysent->sv_size)
+		sa->callp = &nosys_sysent;
+	else
+		sa->callp = &p->p_sysent->sv_table[sa->code];
 
 	KASSERT(sa->callp->sy_narg <= nitems(sa->args),
 	    ("Too many syscall arguments!"));
@@ -1045,7 +1045,7 @@
 	if (sa->callp->sy_narg > regcnt) {
 		params = (caddr_t)frame->tf_rsp + sizeof(register_t);
 		error = copyin(params, &sa->args[regcnt],
-	    	    (sa->callp->sy_narg - regcnt) * sizeof(sa->args[0]));
+		    (sa->callp->sy_narg - regcnt) * sizeof(sa->args[0]));
 		if (__predict_false(error != 0))
 			return (error);
 	}
diff --git a/sys/amd64/ia32/ia32_syscall.c b/sys/amd64/ia32/ia32_syscall.c
--- a/sys/amd64/ia32/ia32_syscall.c
+++ b/sys/amd64/ia32/ia32_syscall.c
@@ -183,7 +183,7 @@
 		params += sizeof(quad_t);
 	}
  	if (sa->code >= p->p_sysent->sv_size)
- 		sa->callp = &p->p_sysent->sv_table[0];
+		sa->callp = &nosys_sysent;
   	else
  		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/amd64/linux/linux_sysvec.c b/sys/amd64/linux/linux_sysvec.c
--- a/sys/amd64/linux/linux_sysvec.c
+++ b/sys/amd64/linux/linux_sysvec.c
@@ -159,7 +159,7 @@
 
 	if (sa->code >= p->p_sysent->sv_size)
 		/* nosys */
-		sa->callp = &p->p_sysent->sv_table[p->p_sysent->sv_size - 1];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/amd64/linux32/linux32_sysvec.c b/sys/amd64/linux32/linux32_sysvec.c
--- a/sys/amd64/linux32/linux32_sysvec.c
+++ b/sys/amd64/linux32/linux32_sysvec.c
@@ -531,7 +531,7 @@
 
 	if (sa->code >= p->p_sysent->sv_size)
 		/* nosys */
-		sa->callp = &p->p_sysent->sv_table[p->p_sysent->sv_size - 1];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/arm/arm/elf_machdep.c b/sys/arm/arm/elf_machdep.c
--- a/sys/arm/arm/elf_machdep.c
+++ b/sys/arm/arm/elf_machdep.c
@@ -87,7 +87,7 @@
 	.sv_maxssiz	= NULL,
 	.sv_flags	=
 			  SV_ASLR | SV_SHP | SV_TIMEKEEP | SV_RNG_SEED_VER |
-			  SV_ABI_FREEBSD | SV_ILP32,
+			  SV_ABI_FREEBSD | SV_ILP32 | SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
diff --git a/sys/arm/arm/syscall.c b/sys/arm/arm/syscall.c
--- a/sys/arm/arm/syscall.c
+++ b/sys/arm/arm/syscall.c
@@ -118,7 +118,7 @@
 	}
 	p = td->td_proc;
 	if (sa->code >= p->p_sysent->sv_size)
-		sa->callp = &p->p_sysent->sv_table[0];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 	error = 0;
diff --git a/sys/arm64/arm64/elf32_machdep.c b/sys/arm64/arm64/elf32_machdep.c
--- a/sys/arm64/arm64/elf32_machdep.c
+++ b/sys/arm64/arm64/elf32_machdep.c
@@ -105,7 +105,7 @@
 	.sv_fixlimit	= NULL, // XXX
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_ABI_FREEBSD | SV_ILP32 | SV_SHP | SV_TIMEKEEP |
-	    SV_RNG_SEED_VER,
+	    SV_RNG_SEED_VER | SV_SIGSYS,
 	.sv_set_syscall_retval = freebsd32_set_syscall_retval,
 	.sv_fetch_syscall_args = freebsd32_fetch_syscall_args,
 	.sv_syscallnames = freebsd32_syscallnames,
@@ -191,7 +191,7 @@
 	}
 
 	if (sa->code >= p->p_sysent->sv_size)
-		sa->callp = &p->p_sysent->sv_table[0];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/arm64/arm64/elf_machdep.c b/sys/arm64/arm64/elf_machdep.c
--- a/sys/arm64/arm64/elf_machdep.c
+++ b/sys/arm64/arm64/elf_machdep.c
@@ -84,7 +84,7 @@
 	.sv_fixlimit	= NULL,
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_SHP | SV_TIMEKEEP | SV_ABI_FREEBSD | SV_LP64 |
-	    SV_ASLR | SV_RNG_SEED_VER,
+	    SV_ASLR | SV_RNG_SEED_VER | SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
diff --git a/sys/arm64/arm64/trap.c b/sys/arm64/arm64/trap.c
--- a/sys/arm64/arm64/trap.c
+++ b/sys/arm64/arm64/trap.c
@@ -151,7 +151,7 @@
 	}
 
 	if (__predict_false(sa->code >= p->p_sysent->sv_size))
-		sa->callp = &p->p_sysent->sv_table[0];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/arm64/linux/linux_sysvec.c b/sys/arm64/linux/linux_sysvec.c
--- a/sys/arm64/linux/linux_sysvec.c
+++ b/sys/arm64/linux/linux_sysvec.c
@@ -123,7 +123,7 @@
 	sa->original_code = sa->code;
 	/* LINUXTODO: generic syscall? */
 	if (sa->code >= p->p_sysent->sv_size)
-		sa->callp = &p->p_sysent->sv_table[0];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/compat/ia32/ia32_sysvec.c b/sys/compat/ia32/ia32_sysvec.c
--- a/sys/compat/ia32/ia32_sysvec.c
+++ b/sys/compat/ia32/ia32_sysvec.c
@@ -127,7 +127,8 @@
 	.sv_fixlimit	= ia32_fixlimit,
 	.sv_maxssiz	= &ia32_maxssiz,
 	.sv_flags	= SV_ABI_FREEBSD | SV_ASLR | SV_IA32 | SV_ILP32 |
-			    SV_SHP | SV_TIMEKEEP | SV_RNG_SEED_VER | SV_DSO_SIG,
+			    SV_SHP | SV_TIMEKEEP | SV_RNG_SEED_VER |
+			    SV_DSO_SIG | SV_SIGSYS,
 	.sv_set_syscall_retval = ia32_set_syscall_retval,
 	.sv_fetch_syscall_args = ia32_fetch_syscall_args,
 	.sv_syscallnames = freebsd32_syscallnames,
diff --git a/sys/i386/i386/elf_machdep.c b/sys/i386/i386/elf_machdep.c
--- a/sys/i386/i386/elf_machdep.c
+++ b/sys/i386/i386/elf_machdep.c
@@ -75,7 +75,7 @@
 	.sv_fixlimit	= NULL,
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_ABI_FREEBSD | SV_ASLR | SV_IA32 | SV_ILP32 |
-			    SV_SHP | SV_TIMEKEEP | SV_RNG_SEED_VER,
+			    SV_SHP | SV_TIMEKEEP | SV_RNG_SEED_VER | SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
diff --git a/sys/i386/i386/trap.c b/sys/i386/i386/trap.c
--- a/sys/i386/i386/trap.c
+++ b/sys/i386/i386/trap.c
@@ -1113,7 +1113,7 @@
 	}
 
  	if (sa->code >= p->p_sysent->sv_size)
- 		sa->callp = &p->p_sysent->sv_table[0];
+		sa->callp = &sysent_nosys;
   	else
  		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/i386/linux/linux_sysvec.c b/sys/i386/linux/linux_sysvec.c
--- a/sys/i386/linux/linux_sysvec.c
+++ b/sys/i386/linux/linux_sysvec.c
@@ -522,7 +522,7 @@
 
 	if (sa->code >= p->p_sysent->sv_size)
 		/* nosys */
-		sa->callp = &p->p_sysent->sv_table[p->p_sysent->sv_size - 1];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/kern/imgact_aout.c b/sys/kern/imgact_aout.c
--- a/sys/kern/imgact_aout.c
+++ b/sys/kern/imgact_aout.c
@@ -91,7 +91,8 @@
 	.sv_setregs	= exec_setregs,
 	.sv_fixlimit	= NULL,
 	.sv_maxssiz	= NULL,
-	.sv_flags	= SV_ABI_FREEBSD | SV_AOUT | SV_IA32 | SV_ILP32,
+	.sv_flags	= SV_ABI_FREEBSD | SV_AOUT | SV_IA32 | SV_ILP32 |
+			    SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
@@ -140,7 +141,8 @@
 	.sv_setregs	= ia32_setregs,
 	.sv_fixlimit	= ia32_fixlimit,
 	.sv_maxssiz	= &ia32_maxssiz,
-	.sv_flags	= SV_ABI_FREEBSD | SV_AOUT | SV_IA32 | SV_ILP32,
+	.sv_flags	= SV_ABI_FREEBSD | SV_AOUT | SV_IA32 | SV_ILP32 |
+			    SV_SIGSYS,
 	.sv_set_syscall_retval = ia32_set_syscall_retval,
 	.sv_fetch_syscall_args = ia32_fetch_syscall_args,
 	.sv_syscallnames = freebsd32_syscallnames,
diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -159,6 +159,10 @@
 SYSCTL_INT(_kern, OID_AUTO, lognosys, CTLFLAG_RWTUN, &kern_lognosys, 0,
     "Log invalid syscalls");
 
+static int	kern_signosys = 1;
+SYSCTL_INT(_kern, OID_AUTO, signosys, CTLFLAG_RWTUN, &kern_signosys, 0,
+    "Send SIGSYS on return from invalid syscall");
+
 __read_frequently bool sigfastblock_fetch_always = false;
 SYSCTL_BOOL(_kern, OID_AUTO, sigfastblock_fetch_always, CTLFLAG_RWTUN,
     &sigfastblock_fetch_always, 0,
@@ -2686,7 +2690,8 @@
 	audited = AUDIT_SYSCALL_ENTER(sc, td) != 0;
 
 	if (!sy_thr_static) {
-		error = syscall_thread_enter(td, se);
+		error = syscall_thread_enter(td, &se);
+		sy_thr_static = (se->sy_thrcnt & SY_THR_STATIC) != 0;
 		if (error != 0) {
 			tsr->ts_ret.sr_error = error;
 			return;
@@ -4218,9 +4223,11 @@
 
 	p = td->td_proc;
 
-	PROC_LOCK(p);
-	tdsignal(td, SIGSYS);
-	PROC_UNLOCK(p);
+	if (SV_PROC_FLAG(p, SV_SIGSYS) != 0 && kern_signosys) {
+		PROC_LOCK(p);
+		tdsignal(td, SIGSYS);
+		PROC_UNLOCK(p);
+	}
 	if (kern_lognosys == 1 || kern_lognosys == 3) {
 		uprintf("pid %d comm %s: nosys %d\n", p->p_pid, p->p_comm,
 		    td->td_sa.code);
diff --git a/sys/kern/kern_syscalls.c b/sys/kern/kern_syscalls.c
--- a/sys/kern/kern_syscalls.c
+++ b/sys/kern/kern_syscalls.c
@@ -61,6 +61,17 @@
 	return (nosys(td, args));
 }
 
+struct sysent nosys_sysent = {
+	.sy_call =	(sy_call_t *)nosys,
+	.sy_systrace_args_func = NULL,
+	.sy_narg =	0,
+	.sy_flags =	SYF_CAPENABLED,
+	.sy_auevent =	AUE_NULL,
+	.sy_entry =	0, /* DTRACE_IDNONE */
+	.sy_return =	0,
+	.sy_thrcnt =	SY_THR_STATIC,
+};
+
 static void
 syscall_thread_drain(struct sysent *se)
 {
@@ -78,19 +89,21 @@
 }
 
 int
-syscall_thread_enter(struct thread *td, struct sysent *se)
+syscall_thread_enter(struct thread *td, struct sysent **se)
 {
 	uint32_t cnt, oldcnt;
 
-	KASSERT((se->sy_thrcnt & SY_THR_STATIC) == 0,
+	KASSERT(((*se)->sy_thrcnt & SY_THR_STATIC) == 0,
 	    ("%s: not a static syscall", __func__));
 
 	do {
-		oldcnt = se->sy_thrcnt;
-		if ((oldcnt & (SY_THR_DRAINING | SY_THR_ABSENT)) != 0)
-			return (ENOSYS);
+		oldcnt = (*se)->sy_thrcnt;
+		if ((oldcnt & (SY_THR_DRAINING | SY_THR_ABSENT)) != 0) {
+			*se = &nosys_sysent;
+			return (0);
+		}
 		cnt = oldcnt + SY_THR_INCR;
-	} while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
+	} while (atomic_cmpset_acq_32(&(*se)->sy_thrcnt, oldcnt, cnt) == 0);
 	return (0);
 }
 
diff --git a/sys/kern/subr_syscall.c b/sys/kern/subr_syscall.c
--- a/sys/kern/subr_syscall.c
+++ b/sys/kern/subr_syscall.c
@@ -144,7 +144,8 @@
 	    AUDIT_SYSCALL_ENTER(sa->code, td) ||
 	    !sy_thr_static)) {
 		if (!sy_thr_static) {
-			error = syscall_thread_enter(td, se);
+			error = syscall_thread_enter(td, &se);
+			sy_thr_static = (se->sy_thrcnt & SY_THR_STATIC) != 0;
 			if (error != 0) {
 				td->td_errno = error;
 				goto retval;
diff --git a/sys/powerpc/powerpc/elf32_machdep.c b/sys/powerpc/powerpc/elf32_machdep.c
--- a/sys/powerpc/powerpc/elf32_machdep.c
+++ b/sys/powerpc/powerpc/elf32_machdep.c
@@ -124,7 +124,7 @@
 #endif
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_ABI_FREEBSD | SV_ILP32 | SV_SHP | SV_ASLR |
-			    SV_TIMEKEEP | SV_RNG_SEED_VER,
+			    SV_TIMEKEEP | SV_RNG_SEED_VER | SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_shared_page_base = FREEBSD32_SHAREDPAGE,
diff --git a/sys/powerpc/powerpc/elf64_machdep.c b/sys/powerpc/powerpc/elf64_machdep.c
--- a/sys/powerpc/powerpc/elf64_machdep.c
+++ b/sys/powerpc/powerpc/elf64_machdep.c
@@ -86,7 +86,7 @@
 	.sv_fixlimit	= NULL,
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_ABI_FREEBSD | SV_LP64 | SV_SHP | SV_ASLR |
-			    SV_TIMEKEEP | SV_RNG_SEED_VER,
+			    SV_TIMEKEEP | SV_RNG_SEED_VER | SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
@@ -128,7 +128,7 @@
 	.sv_fixlimit	= NULL,
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_ABI_FREEBSD | SV_LP64 | SV_SHP |
-			    SV_TIMEKEEP | SV_RNG_SEED_VER,
+			    SV_TIMEKEEP | SV_RNG_SEED_VER | SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
diff --git a/sys/powerpc/powerpc/trap.c b/sys/powerpc/powerpc/trap.c
--- a/sys/powerpc/powerpc/trap.c
+++ b/sys/powerpc/powerpc/trap.c
@@ -694,7 +694,7 @@
 	}
 
 	if (sa->code >= p->p_sysent->sv_size)
-		sa->callp = &p->p_sysent->sv_table[0];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/riscv/riscv/elf_machdep.c b/sys/riscv/riscv/elf_machdep.c
--- a/sys/riscv/riscv/elf_machdep.c
+++ b/sys/riscv/riscv/elf_machdep.c
@@ -84,7 +84,7 @@
 	.sv_fixlimit	= NULL,
 	.sv_maxssiz	= NULL,
 	.sv_flags	= SV_ABI_FREEBSD | SV_LP64 | SV_SHP | SV_TIMEKEEP |
-	    SV_ASLR | SV_RNG_SEED_VER,
+	    SV_ASLR | SV_RNG_SEED_VER | SV_SIGSYS,
 	.sv_set_syscall_retval = cpu_set_syscall_retval,
 	.sv_fetch_syscall_args = cpu_fetch_syscall_args,
 	.sv_syscallnames = syscallnames,
diff --git a/sys/riscv/riscv/trap.c b/sys/riscv/riscv/trap.c
--- a/sys/riscv/riscv/trap.c
+++ b/sys/riscv/riscv/trap.c
@@ -115,7 +115,7 @@
 	}
 
 	if (__predict_false(sa->code >= p->p_sysent->sv_size))
-		sa->callp = &p->p_sysent->sv_table[0];
+		sa->callp = &nosys_sysent;
 	else
 		sa->callp = &p->p_sysent->sv_table[sa->code];
 
diff --git a/sys/sys/sysent.h b/sys/sys/sysent.h
--- a/sys/sys/sysent.h
+++ b/sys/sys/sysent.h
@@ -164,7 +164,7 @@
 #define	SV_IA32		0x004000	/* Intel 32-bit executable. */
 #define	SV_AOUT		0x008000	/* a.out executable. */
 #define	SV_SHP		0x010000	/* Shared page. */
-#define	SV_AVAIL1	0x020000	/* Unused */
+#define	SV_SIGSYS	0x020000	/* SIGSYS for non-existing syscall */
 #define	SV_TIMEKEEP	0x040000	/* Shared page timehands. */
 #define	SV_ASLR		0x080000	/* ASLR allowed. */
 #define	SV_RNG_SEED_VER	0x100000	/* random(4) reseed generation. */
@@ -191,6 +191,7 @@
 extern struct sysentvec aout_sysvec;
 extern struct sysent sysent[];
 extern const char *syscallnames[];
+extern struct sysent nosys_sysent;
 
 struct nosys_args {
 	register_t dummy;
@@ -319,7 +320,7 @@
 int	lkmnosys(struct thread *, struct nosys_args *);
 int	lkmressys(struct thread *, struct nosys_args *);
 
-int	syscall_thread_enter(struct thread *td, struct sysent *se);
+int	syscall_thread_enter(struct thread *td, struct sysent **se);
 void	syscall_thread_exit(struct thread *td, struct sysent *se);
 
 int shared_page_alloc(int size, int align);
diff --git a/tests/sys/kern/Makefile b/tests/sys/kern/Makefile
--- a/tests/sys/kern/Makefile
+++ b/tests/sys/kern/Makefile
@@ -48,6 +48,7 @@
 ATF_TESTS_C+=	unix_socketpair_test
 ATF_TESTS_C+=	waitpid_nohang
 ATF_TESTS_C+=	pdeathsig
+ATF_TESTS_C+=	sigsys
 
 ATF_TESTS_SH+=	coredump_phnum_test
 ATF_TESTS_SH+=	sonewconn_overflow
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 +1,69 @@
+/*-
+ * Copyright (c) 2023 The FreeBSD Foundation
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * This software were developed by Konstantin Belousov <kib@FreeBSD.org>
+ * under sponsorship from the FreeBSD Foundation.
+ */
+
+#include <sys/syscall.h>
+
+#include <atf-c.h>
+#include <errno.h>
+#include <signal.h>
+#include <stdatomic.h>
+#include <stdbool.h>
+
+static sig_atomic_t sigsys_cnt;
+
+static void
+sigsys_handler(int signo, siginfo_t *si, void *ucp)
+{
+	sigsys_cnt++;
+}
+
+ATF_TC(sigsys_test);
+
+ATF_TC_HEAD(sigsys_test, tc)
+{
+	atf_tc_set_md_var(tc, "descr",
+	    "Testing delivery of SIGSYS on invalid syscalls");
+}
+
+ATF_TC_BODY(sigsys_test, tc)
+{
+	struct sigaction sa;
+
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_sigaction = sigsys_handler;
+	sa.sa_flags = SA_SIGINFO;
+	ATF_REQUIRE(sigaction(SIGSYS, &sa, NULL) == 0);
+
+	ATF_REQUIRE(syscall(273) == -1);	/* reserved */
+	ATF_CHECK_ERRNO(ENOSYS, true);
+	atomic_signal_fence(memory_order_seq_cst);
+	ATF_CHECK_EQ(1, sigsys_cnt);
+
+	ATF_REQUIRE(syscall(440) == -1);	/* SYS_kse_switchin */
+	ATF_CHECK_ERRNO(ENOSYS, true);
+	atomic_signal_fence(memory_order_seq_cst);
+	ATF_CHECK_EQ(2, sigsys_cnt);
+
+	/* Hope this is enough for say next two months */
+	ATF_REQUIRE(syscall(3000000) == -1);
+	ATF_CHECK_ERRNO(ENOSYS, true);
+	atomic_signal_fence(memory_order_seq_cst);
+	ATF_CHECK_EQ(3, sigsys_cnt);
+
+	ATF_REQUIRE(syscall(SYS_afs3_syscall) == -1);
+	ATF_CHECK_ERRNO(ENOSYS, true);
+	atomic_signal_fence(memory_order_seq_cst);
+	ATF_CHECK_EQ(4, sigsys_cnt);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, sigsys_test);
+	return (atf_no_error());
+}