*/
        rt2x00pci_register_read(rt2x00dev, BCNCSR1, ®);
        rt2x00_set_field32(®, BCNCSR1_PRELOAD,
-                          PREAMBLE + get_duration(IEEE80211_HEADER, 2));
+                          PREAMBLE + get_duration(IEEE80211_HEADER, 20));
        rt2x00pci_register_write(rt2x00dev, BCNCSR1, reg);
 
        /*
 
         */
        rt2x00pci_register_read(rt2x00dev, BCNCSR1, ®);
        rt2x00_set_field32(®, BCNCSR1_PRELOAD,
-                          PREAMBLE + get_duration(IEEE80211_HEADER, 2));
+                          PREAMBLE + get_duration(IEEE80211_HEADER, 20));
        rt2x00_set_field32(®, BCNCSR1_BEACON_CWMIN,
                           rt2x00lib_get_ring(rt2x00dev,
                                              IEEE80211_TX_QUEUE_BEACON)
 
         */
        rt2500usb_register_read(rt2x00dev, TXRX_CSR20, ®);
        rt2x00_set_field16(®, 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(®, TXRX_CSR20_BCN_EXPECT_WINDOW, 0);
        else