diff --git a/sys/i386/isa/clock.c b/sys/i386/isa/clock.c
index f2de4f5d6b04..3125bd1b411c 100644
--- a/sys/i386/isa/clock.c
+++ b/sys/i386/isa/clock.c
@@ -579,6 +579,7 @@ rtc_restore(void)
 
 	/* Restore all of the RTC's "status" (actually, control) registers. */
 	/* XXX locking is needed for RTC access. */
+	rtc_reg = -1;
 	writertc(RTC_STATUSB, RTCSB_24HR);
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, rtc_statusb);
diff --git a/sys/isa/atrtc.c b/sys/isa/atrtc.c
index f2de4f5d6b04..3125bd1b411c 100644
--- a/sys/isa/atrtc.c
+++ b/sys/isa/atrtc.c
@@ -579,6 +579,7 @@ rtc_restore(void)
 
 	/* Restore all of the RTC's "status" (actually, control) registers. */
 	/* XXX locking is needed for RTC access. */
+	rtc_reg = -1;
 	writertc(RTC_STATUSB, RTCSB_24HR);
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, rtc_statusb);