PECT_OK(kill(me, SIGUSR1));
-  EXPECT_EQ(1, had_signal);
+  EXPECT_EQ(1, signal_cnt);
+
+  union sigval sv;
+  sv.sival_int = 0x1234;
+  EXPECT_CAPMODE(sigqueue(child, SIGUSR1, sv));
+  EXPECT_OK(sigqueue(me, SIGUSR1, sv));
+  EXPECT_EQ(2, signal_cnt);
 
   signal(SIGUSR1, original);
 }
diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 91361d680809..7f399586f639 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -2047,6 +2047,16 @@ kern_sigqueue(struct thread *td, pid_t pid, int signumf, union sigval *value)
 	if (pid <= 0)
 		return (EINVAL);
 
+	/*
+	 * A process in capability mode can send signals only to itself.
+	 */
+	if (pid != td->td_proc->p_pid) {
+		if (CAP_TRACING(td))
+			ktrcapfail(CAPFAIL_SIGNAL, &signum);
+		if (IN_CAPABILITY_MODE(td))
+			return (ECAPMODE);
+	}
+
 	if ((signumf & __SIGQUEUE_TID) == 0) {
 		if ((p = pfind_any(pid)) == NULL)
 			return (ESRCH);