diff --git a/sys/x86/isa/atrtc.c b/sys/x86/isa/atrtc.c
--- a/sys/x86/isa/atrtc.c
+++ b/sys/x86/isa/atrtc.c
@@ -79,6 +79,7 @@
 
 int	atrtcclock_disable = 0;
 
+static	int	rtc_century = 0;
 static	int	rtc_reg = -1;
 static	u_char	rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
 static	u_char	rtc_statusb = RTCSB_24HR;
@@ -420,6 +421,31 @@
 #endif
 }
 
+static int
+rtc_acpi_century_get(void)
+{
+#ifdef DEV_ACPI
+	ACPI_TABLE_FADT *fadt;
+	vm_paddr_t physaddr;
+	int century;
+
+	physaddr = acpi_find_table(ACPI_SIG_FADT);
+	if (physaddr == 0)
+		return (0);
+
+	fadt = acpi_map_table(physaddr, ACPI_SIG_FADT);
+	if (fadt == NULL)
+		return (0);
+
+	century = fadt->Century;
+	acpi_unmap_table(fadt);
+
+	return century;
+#else
+	return (0);
+#endif
+}
+
 static int
 atrtc_probe(device_t dev)
 {
@@ -435,6 +461,7 @@
 		device_set_desc(dev, "AT realtime clock");
 		return (BUS_PROBE_LOW_PRIORITY);
 	}
+	rtc_century = rtc_acpi_century_get();
 	return (result);
 }
 
@@ -548,9 +575,8 @@
 	rtcout_locked(RTC_DAY,   bct.day);
 	rtcout_locked(RTC_MONTH, bct.mon);
 	rtcout_locked(RTC_YEAR,  bct.year & 0xff);
-#ifdef USE_RTC_CENTURY
-	rtcout_locked(RTC_CENTURY, bct.year >> 8);
-#endif
+	if (rtc_century)
+		rtcout_locked(rtc_century, bct.year >> 8);
 
 	/*
 	 * Re-enable RTC updates and interrupts.
@@ -592,9 +618,8 @@
 	bct.day  = rtcin_locked(RTC_DAY);
 	bct.mon  = rtcin_locked(RTC_MONTH);
 	bct.year = rtcin_locked(RTC_YEAR);
-#ifdef USE_RTC_CENTURY
-	bct.year |= rtcin_locked(RTC_CENTURY) << 8;
-#endif
+	if (rtc_century)
+		bct.year |= rtcin_locked(rtc_century) << 8;
 	mtx_unlock_spin(&atrtc_lock);
 	mtx_unlock(&atrtc_time_lock);
 	/* dow is unused in timespec conversion and we have no nsec info. */