diff --git a/target/linux/ramips/files/drivers/net/ethernet/ralink/mtk_eth_soc.c b/target/linux/ramips/files/drivers/net/ethernet/ralink/mtk_eth_soc.c
index ad0ade4646..20a75842ab 100644
--- a/target/linux/ramips/files/drivers/net/ethernet/ralink/mtk_eth_soc.c
+++ b/target/linux/ramips/files/drivers/net/ethernet/ralink/mtk_eth_soc.c
@@ -564,7 +564,7 @@ static inline u32 fe_empty_txd(struct fe_tx_ring *ring)
 	barrier();
 	return (u32)(ring->tx_ring_size -
 			((ring->tx_next_idx - ring->tx_free_idx) &
-			 (ring->tx_ring_size - 1)));
+			 (ring->tx_ring_size - 1)) - 1);
 }
 
 struct fe_map_state {