Index: share/man/man3/Makefile
===================================================================
--- share/man/man3/Makefile
+++ share/man/man3/Makefile
@@ -299,6 +299,7 @@
 		stdarg.3 va_start.3
 MLINKS+=	timeradd.3 timerclear.3 \
 		timeradd.3 timercmp.3 \
+		timeradd.3 timerisvalid.3 \
 		timeradd.3 timerisset.3 \
 		timeradd.3 timersub.3 \
 		timeradd.3 timespecadd.3 \
Index: share/man/man3/timeradd.3
===================================================================
--- share/man/man3/timeradd.3
+++ share/man/man3/timeradd.3
@@ -27,13 +27,14 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd July 30, 2018
+.Dd June 30, 2020
 .Dt TIMERADD 3
 .Os
 .Sh NAME
 .Nm timeradd ,
 .Nm timersub ,
 .Nm timerclear ,
+.Nm timeisvalid,
 .Nm timerisset ,
 .Nm timercmp ,
 .Nm timespecadd ,
@@ -51,6 +52,8 @@
 .Ft void
 .Fn timerclear "struct timeval *tvp"
 .Ft int
+.Fn timerisvalid "struct timespec *a"
+.Ft int
 .Fn timerisset "struct timeval *tvp"
 .Ft int
 .Fn timercmp "struct timeval *a" "struct timeval *b" CMP
@@ -130,6 +133,11 @@
 .Fn timespecclear
 initialize their argument to midnight (0 hour) January 1st, 1970 (the Epoch).
 .Pp
+.Fn timerisvalid a
+tests if the microsecond value in
+.Fa a
+is greater than or equal to zero and less than one million.
+.Pp
 .Fn timerisset
 and
 .Fn timespecisset
Index: sys/sys/time.h
===================================================================
--- sys/sys/time.h
+++ sys/sys/time.h
@@ -434,6 +434,8 @@
 			(vvp)->tv_usec += 1000000;			\
 		}							\
 	} while (0)
+#define timerisvalid(tvp)                                               \
+	((tvp)->tv_usec >= 0 && (tvp)->tv_usec < 1000000)
 #endif
 
 /*