diff --git a/kern/kern_ntptime.c b/kern/kern_ntptime.c
--- a/kern/kern_ntptime.c
+++ b/kern/kern_ntptime.c
@@ -262,8 +262,8 @@
 	0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", "");
 
 #ifdef PPS_SYNC
-SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RW, &pps_shiftmax, 0, "");
-SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shift, CTLFLAG_RW, &pps_shift, 0, "");
+SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RD, &pps_shiftmax, 0, "");
+SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shift, CTLFLAG_RD, &pps_shift, 0, "");
 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, time_monitor, CTLFLAG_RD, &time_monitor, 0, "");
 
 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, &pps_freq, sizeof(pps_freq), "I", "");