diff --git a/drivers/net/wireless/wl12xx/wl1271_tx.c b/drivers/net/wireless/wl12xx/wl1271_tx.c
index 5d3aa4b26cf3782c59e05aa47aa709029a7608e5..56a7f36380b7a76ce7db3c32e43a600ce6a85608 100644
--- a/drivers/net/wireless/wl12xx/wl1271_tx.c
+++ b/drivers/net/wireless/wl12xx/wl1271_tx.c
@@ -57,8 +57,8 @@ static int wl1271_tx_allocate(struct wl1271 *wl, struct sk_buff *skb, u32 extra)
 	/* approximate the number of blocks required for this packet
 	   in the firmware */
 	/* FIXME: try to figure out what is done here and make it cleaner */
-	total_blocks = (total_len) >> TX_HW_BLOCK_SHIFT_DIV;
-	excluded = (total_blocks << 2) + (skb->len & 0xff) + 34;
+	total_blocks = (total_len + 20) >> TX_HW_BLOCK_SHIFT_DIV;
+	excluded = (total_blocks << 2) + ((total_len + 20) & 0xff) + 34;
 	total_blocks += (excluded > 252) ? 2 : 1;
 	total_blocks += TX_HW_BLOCK_SPARE;