diff --git a/port.c b/port.c
index 3984b78..ef2686d 100644
--- a/port.c
+++ b/port.c
@@ -163,10 +163,15 @@ static int msg_current(struct ptp_message *m, struct timespec now)
 	t1 = m->ts.host.tv_sec * NSEC2SEC + m->ts.host.tv_nsec;
 	t2 = now.tv_sec * NSEC2SEC + now.tv_nsec;
 
-	if (m->header.logMessageInterval < 0)
+	if (m->header.logMessageInterval < -63) {
+		tmo = 0;
+	} else if (m->header.logMessageInterval > 31) {
+		tmo = INT64_MAX;
+	} else if (m->header.logMessageInterval < 0) {
 		tmo = 4LL * NSEC2SEC / (1 << -m->header.logMessageInterval);
-	else
+	} else {
 		tmo = 4LL * (1 << m->header.logMessageInterval) * NSEC2SEC;
+	}
 
 	return t2 - t1 < tmo;
 }