Index: kern_resource.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_resource.c,v
retrieving revision 1.181
diff -p -u -r1.181 kern_resource.c
--- kern_resource.c	13 May 2018 14:45:23 -0000	1.181
+++ kern_resource.c	14 Mar 2019 00:24:26 -0000
@@ -488,7 +488,7 @@ void
 calcru(struct proc *p, struct timeval *up, struct timeval *sp,
     struct timeval *ip, struct timeval *rp)
 {
-	uint64_t u, st, ut, it, tot;
+	uint64_t u, st, ut, it, tot, dt;
 	struct lwp *l;
 	struct bintime tm;
 	struct timeval tv;
@@ -549,10 +549,12 @@ calcru(struct proc *p, struct timeval *u
 	 * which must have increased.
 	 */
 	if (p->p_xutime > ut) {
-		st -= p->p_xutime - ut;
+		dt = p->p_xutime - ut;
+		st -= uimin(dt, st);
 		ut = p->p_xutime;
 	} else if (p->p_xstime > st) {
-		ut -= p->p_xstime - st;
+		dt = p->p_xstime - st;
+		ut -= uimin(dt, ut);
 		st = p->p_xstime;
 	}