diff --git a/include/iscsi-private.h b/include/iscsi-private.h
index 7d37b20..d57d5a2 100644
--- a/include/iscsi-private.h
+++ b/include/iscsi-private.h
@@ -182,6 +182,7 @@ struct iscsi_pdu {
 	uint32_t lun;
 	uint32_t itt;
 	uint32_t cmdsn;
+	uint32_t datasn;
 	enum iscsi_opcode response_opcode;
 
 	iscsi_command_cb callback;
diff --git a/lib/scsi-command.c b/lib/scsi-command.c
index aa1682e..bad64ac 100644
--- a/lib/scsi-command.c
+++ b/lib/scsi-command.c
@@ -120,7 +120,7 @@ iscsi_send_data_out(struct iscsi_context *iscsi, struct iscsi_pdu *cmd_pdu,
 		iscsi_pdu_set_expstatsn(pdu, iscsi->statsn+1);
 
 		/* data sn */
-		iscsi_pdu_set_datasn(pdu, 0);
+		iscsi_pdu_set_datasn(pdu, cmd_pdu->datasn++);
 
 		/* buffer offset */
 		iscsi_pdu_set_bufferoffset(pdu, offset);