diff -up dhcp-4.3.0a1/common/dispatch.c.interval dhcp-4.3.0a1/common/dispatch.c
--- dhcp-4.3.0a1/common/dispatch.c.interval	2013-12-20 13:51:14.385260622 +0100
+++ dhcp-4.3.0a1/common/dispatch.c	2013-12-20 13:51:14.493259116 +0100
@@ -343,7 +343,20 @@ void add_timeout (when, where, what, ref
 	q->next  = timeouts;
 	timeouts = q;
 
-	isc_interval_set(&interval, sec & DHCP_SEC_MAX, usec * 1000);
+	/* isc_time_nowplusinterval() is not safe with 64-bit time_t and will
+	 * return an error for sufficiently large intervals.  We have to limit
+	 * the interval to INT_MAX or less to ensure the interval doesn't
+	 * overflow 32 bits, since the returned isc_time_t fields are
+	 * 32-bit unsigned ints.
+	 *
+	 * HACK: The 9 is a magic number of seconds, since some time may have
+	 * gone by since the last call to gettimeofday() and the one in
+	 * isc_time_nowplusinterval().
+	 */
+	if (sec > TIME_MAX)
+		sec = TIME_MAX - 9;
+
+	isc_interval_set(&interval, sec, usec * 1000);
 	status = isc_time_nowplusinterval(&expires, &interval);
 	if (status != ISC_R_SUCCESS) {
 		/*