diff --git a/drivers/net/wireless/rt2x00/rt2400pci.c b/drivers/net/wireless/rt2x00/rt2400pci.c
index 0e34565..bfab5a1 100644
--- a/drivers/net/wireless/rt2x00/rt2400pci.c
+++ b/drivers/net/wireless/rt2x00/rt2400pci.c
@@ -277,7 +277,7 @@
 	 */
 	rt2x00pci_register_read(rt2x00dev, BCNCSR1, &reg);
 	rt2x00_set_field32(&reg, BCNCSR1_PRELOAD,
-			   PREAMBLE + get_duration(IEEE80211_HEADER, 2));
+			   PREAMBLE + get_duration(IEEE80211_HEADER, 20));
 	rt2x00pci_register_write(rt2x00dev, BCNCSR1, reg);
 
 	/*
diff --git a/drivers/net/wireless/rt2x00/rt2500pci.c b/drivers/net/wireless/rt2x00/rt2500pci.c
index fa8669f..c8c6a84 100644
--- a/drivers/net/wireless/rt2x00/rt2500pci.c
+++ b/drivers/net/wireless/rt2x00/rt2500pci.c
@@ -277,7 +277,7 @@
 	 */
 	rt2x00pci_register_read(rt2x00dev, BCNCSR1, &reg);
 	rt2x00_set_field32(&reg, BCNCSR1_PRELOAD,
-			   PREAMBLE + get_duration(IEEE80211_HEADER, 2));
+			   PREAMBLE + get_duration(IEEE80211_HEADER, 20));
 	rt2x00_set_field32(&reg, BCNCSR1_BEACON_CWMIN,
 			   rt2x00lib_get_ring(rt2x00dev,
 					      IEEE80211_TX_QUEUE_BEACON)
diff --git a/drivers/net/wireless/rt2x00/rt2500usb.c b/drivers/net/wireless/rt2x00/rt2500usb.c
index 6d5444b..c70c677 100644
--- a/drivers/net/wireless/rt2x00/rt2500usb.c
+++ b/drivers/net/wireless/rt2x00/rt2500usb.c
@@ -280,7 +280,7 @@
 	 */
 	rt2500usb_register_read(rt2x00dev, TXRX_CSR20, &reg);
 	rt2x00_set_field16(&reg, TXRX_CSR20_OFFSET,
-			   (PREAMBLE + get_duration(IEEE80211_HEADER, 2)) >> 6);
+			   (PREAMBLE + get_duration(IEEE80211_HEADER, 20)) >> 6);
 	if (type == IEEE80211_IF_TYPE_STA)
 		rt2x00_set_field16(&reg, TXRX_CSR20_BCN_EXPECT_WINDOW, 0);
 	else