diff --git a/lib/libc/sys/kqueue.2 b/lib/libc/sys/kqueue.2
--- a/lib/libc/sys/kqueue.2
+++ b/lib/libc/sys/kqueue.2
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd October 8, 2020
+.Dd May 26, 2021
 .Dt KQUEUE 2
 .Os
 .Sh NAME
@@ -762,6 +762,8 @@
 A cancellation request was delivered to the thread, but not yet handled.
 .It Bq Er EINVAL
 The specified time limit or filter is invalid.
+.It Bq Er EINVAL
+The specified length of the event or change lists is negative.
 .It Bq Er ENOENT
 The event could not be found to be modified or deleted.
 .It Bq Er ENOMEM
diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -1303,6 +1303,9 @@
 	struct kevent *kevp, *changes;
 	int i, n, nerrors, error;
 
+	if (nchanges < 0)
+		return (EINVAL);
+
 	nerrors = 0;
 	while (nchanges > 0) {
 		n = nchanges > KQ_NEVENTS ? KQ_NEVENTS : nchanges;
@@ -1887,6 +1890,10 @@
 
 	if (maxevents == 0)
 		goto done_nl;
+	if (maxevents < 0) {
+		error = EINVAL;
+		goto done_nl;
+	}
 
 	rsbt = 0;
 	if (tsp != NULL) {