diff --git a/drivers/net/wireless/rt2x00/rt2400pci.c b/drivers/net/wireless/rt2x00/rt2400pci.c
index 0e345659f42190e4ce4622b277f34a88f81a8f8f..bfab5a165b7633452860a38f66a326072d78f616 100644
--- a/drivers/net/wireless/rt2x00/rt2400pci.c
+++ b/drivers/net/wireless/rt2x00/rt2400pci.c
@@ -277,7 +277,7 @@ static void rt2400pci_config_type(struct rt2x00_dev *rt2x00dev, const int type,
 	 */
 	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 fa8669f5c965fd7a9aabdc7d93ae7c164658d904..c8c6a848be9729544a006d336714834f1ecd2d36 100644
--- a/drivers/net/wireless/rt2x00/rt2500pci.c
+++ b/drivers/net/wireless/rt2x00/rt2500pci.c
@@ -277,7 +277,7 @@ static void rt2500pci_config_type(struct rt2x00_dev *rt2x00dev, const int type,
 	 */
 	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 6d5444b58e6cffe2626b0eea0d864c0d47c9b7c0..c70c677b3f73b7746e60eeb5fbfb5decf15ea2d8 100644
--- a/drivers/net/wireless/rt2x00/rt2500usb.c
+++ b/drivers/net/wireless/rt2x00/rt2500usb.c
@@ -280,7 +280,7 @@ static void rt2500usb_config_type(struct rt2x00_dev *rt2x00dev, const int type,
 	 */
 	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