Index: lib/libc/sys/clock_gettime.2
===================================================================
--- lib/libc/sys/clock_gettime.2
+++ lib/libc/sys/clock_gettime.2
@@ -138,6 +138,8 @@
 was not a valid value.
 .It Bq Er EPERM
 A user other than the super-user attempted to set the time.
+.It Bq Er EINVAL
+Timespec value is invalid.
 .El
 .Sh SEE ALSO
 .Xr date 1 ,
Index: lib/libc/sys/gettimeofday.2
===================================================================
--- lib/libc/sys/gettimeofday.2
+++ lib/libc/sys/gettimeofday.2
@@ -112,6 +112,8 @@
 .Bl -tag -width Er
 .It Bq Er EPERM
 A user other than the super-user attempted to set the time.
+.It Bq Er EINVAL
+Timeval value is invalid.
 .El
 .Sh SEE ALSO
 .Xr date 1 ,
Index: sys/kern/kern_time.c
===================================================================
--- sys/kern/kern_time.c
+++ sys/kern/kern_time.c
@@ -398,7 +398,8 @@
 		return (error);
 	if (clock_id != CLOCK_REALTIME)
 		return (EINVAL);
-	if (ats->tv_nsec < 0 || ats->tv_nsec >= 1000000000)
+	if (ats->tv_nsec < 0 || ats->tv_nsec >= 1000000000
+	    || ats->tv_sec < 0)
 		return (EINVAL);
 	/* XXX Don't convert nsec->usec and back */
 	TIMESPEC_TO_TIMEVAL(&atv, ats);
@@ -618,7 +619,8 @@
 		return (error);
 	/* Verify all parameters before changing time. */
 	if (tv) {
-		if (tv->tv_usec < 0 || tv->tv_usec >= 1000000)
+		if (tv->tv_usec < 0 || tv->tv_usec >= 1000000
+		    || tv->tv_sec < 0)
 			return (EINVAL);
 		error = settime(td, tv);
 	}