diff --git a/drivers/net/mlx4/mlx4_rxtx.c b/drivers/net/mlx4/mlx4_rxtx.c
index ae37f9b..4a77be8 100644
--- a/drivers/net/mlx4/mlx4_rxtx.c
+++ b/drivers/net/mlx4/mlx4_rxtx.c
@@ -233,9 +233,9 @@ mlx4_txq_complete(struct txq *txq)
  *   Index in memory pool (MP) where to add memory region (MR)
  *
  * @return
- *   Added mr->lkey on success, (uint32_t)-1 on failure.
+ *   Added mr->lkey (rte_be32_t) on success, (uint32_t)-1 on failure.
  */
-uint32_t mlx4_txq_add_mr(struct txq *txq, struct rte_mempool *mp, uint32_t i)
+rte_be32_t mlx4_txq_add_mr(struct txq *txq, struct rte_mempool *mp, uint32_t i)
 {
 	struct ibv_mr *mr;
 
@@ -260,9 +260,9 @@ uint32_t mlx4_txq_add_mr(struct txq *txq, struct rte_mempool *mp, uint32_t i)
 	/* Store the new entry. */
 	txq->mp2mr[i].mp = mp;
 	txq->mp2mr[i].mr = mr;
-	txq->mp2mr[i].lkey = mr->lkey;
+	txq->mp2mr[i].lkey = rte_cpu_to_be_32(mr->lkey);
 	DEBUG("%p: new MR lkey for MP \"%s\" (%p): 0x%08" PRIu32,
-	      (void *)txq, mp->name, (void *)mp, txq->mp2mr[i].lkey);
+	      (void *)txq, mp->name, (void *)mp, mr->lkey);
 	return txq->mp2mr[i].lkey;
 }
 
@@ -289,7 +289,6 @@ mlx4_post_send(struct txq *txq, struct rte_mbuf *pkt)
 		uint16_t flags16[2];
 	} srcrb;
 	uint32_t head_idx = sq->head & sq->txbb_cnt_mask;
-	uint32_t lkey;
 	uintptr_t addr;
 	uint32_t owner_opcode = MLX4_OPCODE_SEND;
 	uint32_t byte_count;
@@ -323,10 +322,10 @@ mlx4_post_send(struct txq *txq, struct rte_mbuf *pkt)
 		if (unlikely(dseg >= (struct mlx4_wqe_data_seg *)sq->eob))
 			dseg = (struct mlx4_wqe_data_seg *)sq->buf;
 		dseg->addr = rte_cpu_to_be_64(addr);
-		/* Memory region key for this memory pool. */
-		lkey = mlx4_txq_mp2mr(txq, mlx4_txq_mb2mp(buf));
+		/* Memory region key (big endian) for this memory pool. */
+		dseg->lkey = mlx4_txq_mp2mr(txq, mlx4_txq_mb2mp(buf));
 #ifndef NDEBUG
-		if (unlikely(lkey == (uint32_t)-1)) {
+		if (unlikely(dseg->lkey == rte_cpu_to_be_32((uint32_t)-1))) {
 			/* MR does not exist. */
 			DEBUG("%p: unable to get MP <-> MR association",
 			      (void *)txq);
@@ -341,7 +340,6 @@ mlx4_post_send(struct txq *txq, struct rte_mbuf *pkt)
 			return -EFAULT;
 		}
 #endif /* NDEBUG */
-		dseg->lkey = rte_cpu_to_be_32(lkey);
 		if (likely(buf->data_len)) {
 			byte_count = rte_cpu_to_be_32(buf->data_len);
 		} else {
diff --git a/drivers/net/mlx4/mlx4_rxtx.h b/drivers/net/mlx4/mlx4_rxtx.h
index 719ef45..b1e8ac4 100644
--- a/drivers/net/mlx4/mlx4_rxtx.h
+++ b/drivers/net/mlx4/mlx4_rxtx.h
@@ -135,7 +135,7 @@ struct txq {
 	struct {
 		const struct rte_mempool *mp; /**< Cached memory pool. */
 		struct ibv_mr *mr; /**< Memory region (for mp). */
-		uint32_t lkey; /**< mr->lkey copy. */
+		rte_be32_t lkey; /**< mr->lkey copy. (big endian) */
 	} mp2mr[MLX4_PMD_TX_MP_CACHE]; /**< MP to MR translation table. */
 	struct priv *priv; /**< Back pointer to private data. */
 	unsigned int socket; /**< CPU socket ID for allocations. */
@@ -169,7 +169,7 @@ uint16_t mlx4_tx_burst_removed(void *dpdk_txq, struct rte_mbuf **pkts,
 			       uint16_t pkts_n);
 uint16_t mlx4_rx_burst_removed(void *dpdk_rxq, struct rte_mbuf **pkts,
 			       uint16_t pkts_n);
-uint32_t mlx4_txq_add_mr(struct txq *txq, struct rte_mempool *mp,
+rte_be32_t mlx4_txq_add_mr(struct txq *txq, struct rte_mempool *mp,
 				unsigned int i);
 
 /* mlx4_txq.c */
@@ -207,9 +207,9 @@ mlx4_txq_mb2mp(struct rte_mbuf *buf)
  *   Memory pool for which a memory region lkey must be returned.
  *
  * @return
- *   mr->lkey on success, (uint32_t)-1 on failure.
+ *   mr->lkey (rte_be32_t) on success, (uint32_t)-1 on failure.
  */
-static __rte_always_inline uint32_t
+static __rte_always_inline rte_be32_t
 mlx4_txq_mp2mr(struct txq *txq, struct rte_mempool *mp)
 {
 	unsigned int i;
@@ -220,8 +220,10 @@ mlx4_txq_mp2mr(struct txq *txq, struct rte_mempool *mp)
 			break;
 		}
 		if (txq->mp2mr[i].mp == mp) {
-			assert(txq->mp2mr[i].lkey != (uint32_t)-1);
-			assert(txq->mp2mr[i].mr->lkey == txq->mp2mr[i].lkey);
+			assert(txq->mp2mr[i].lkey !=
+				rte_cpu_to_be_32((uint32_t)-1));
+			assert(txq->mp2mr[i].mr->lkey ==
+				rte_be_to_cpu_32(txq->mp2mr[i].lkey));
 			return txq->mp2mr[i].lkey;
 		}
 	}
