diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index 282692c..c49d1fb 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -65,8 +65,7 @@
 {
 	if (buffer->unmap_len) {
 		struct device *dma_dev = &tx_queue->efx->pci_dev->dev;
-		dma_addr_t unmap_addr = (buffer->dma_addr + buffer->len -
-					 buffer->unmap_len);
+		dma_addr_t unmap_addr = buffer->dma_addr - buffer->dma_offset;
 		if (buffer->flags & EFX_TX_BUF_MAP_SINGLE)
 			dma_unmap_single(dma_dev, unmap_addr, buffer->unmap_len,
 					 DMA_TO_DEVICE);
@@ -414,6 +413,7 @@
 		/* Transfer ownership of the unmapping to the final buffer */
 		buffer->flags = EFX_TX_BUF_CONT | dma_flags;
 		buffer->unmap_len = unmap_len;
+		buffer->dma_offset = buffer->dma_addr - unmap_addr;
 		unmap_len = 0;
 
 		/* Get address and size of next fragment */
@@ -980,6 +980,7 @@
 			return -ENOMEM;
 		}
 		buffer->unmap_len = buffer->len;
+		buffer->dma_offset = 0;
 		buffer->flags |= EFX_TX_BUF_MAP_SINGLE;
 	}
 
@@ -1121,6 +1122,7 @@
 	if (st->in_len == 0) {
 		/* Transfer ownership of the DMA mapping */
 		buffer->unmap_len = st->unmap_len;
+		buffer->dma_offset = buffer->unmap_len - buffer->len;
 		buffer->flags |= st->dma_flags;
 		st->unmap_len = 0;
 	}
@@ -1219,6 +1221,7 @@
 		if (is_last) {
 			buffer->flags = EFX_TX_BUF_CONT | EFX_TX_BUF_MAP_SINGLE;
 			buffer->unmap_len = st->header_unmap_len;
+			buffer->dma_offset = 0;
 			/* Ensure we only unmap them once in case of a
 			 * later DMA mapping error and rollback
 			 */