diff --git a/sys/dev/ath/ath_hal/ar5212/ar5212_beacon.c b/sys/dev/ath/ath_hal/ar5212/ar5212_beacon.c
index a411d3181f50..b52077f10d32 100644
--- a/sys/dev/ath/ath_hal/ar5212/ar5212_beacon.c
+++ b/sys/dev/ath/ath_hal/ar5212/ar5212_beacon.c
@@ -46,10 +46,19 @@ ar5212SetBeaconTimers(struct ath_hal *ah, const HAL_BEACON_TIMERS *bt)
 {
 	struct ath_hal_5212 *ahp = AH5212(ah);
 
-	OS_REG_WRITE(ah, AR_TIMER0, bt->bt_nexttbtt);
-	OS_REG_WRITE(ah, AR_TIMER1, bt->bt_nextdba);
-	OS_REG_WRITE(ah, AR_TIMER2, bt->bt_nextswba);
-	OS_REG_WRITE(ah, AR_TIMER3, bt->bt_nextatim);
+	/*
+	 * Limit the timers to their specific resolutions:
+	 *
+	 * + Timer 0 - 0..15 0xffff TU
+	 * + Timer 1 - 0..18 0x7ffff TU/8
+	 * + Timer 2 - 0..24 0x1ffffff TU/8
+	 * + Timer 3 - 0..15 0xffff TU
+	 */
+	OS_REG_WRITE(ah, AR_TIMER0, bt->bt_nexttbtt & 0xffff);
+	OS_REG_WRITE(ah, AR_TIMER1, bt->bt_nextdba & 0x7ffff);
+	OS_REG_WRITE(ah, AR_TIMER2, bt->bt_nextswba & 0x1ffffff);
+	/* XXX force nextatim to be non-zero? */
+	OS_REG_WRITE(ah, AR_TIMER3, bt->bt_nextatim & 0xffff);
 	/*
 	 * Set the Beacon register after setting all timers.
 	 */