diff --git a/include/haproxy/mux_quic-t.h b/include/haproxy/mux_quic-t.h
index 4dc86d2ee..2dff82835 100644
--- a/include/haproxy/mux_quic-t.h
+++ b/include/haproxy/mux_quic-t.h
@@ -228,9 +228,8 @@ struct qcs {
 		uint64_t bytes;    /* number of bytes sent */
 		uint64_t ack_offset; /* last acked ordered byte offset */
 		struct eb_root acked_frms; /* acked frames ordered by their offsets */
-		struct buffer buf; /* transmit buffer, always valid (buf_empty or real buffer) */
-		struct buffer mbuf[QCC_MBUF_CNT];
-		uint64_t left;     /* data currently stored in mbuf waiting for send */
+		struct buffer buf;      /* transmit buffer before sending via xprt */
+		struct buffer xprt_buf; /* buffer for xprt sending, cleared on ACK. */
 	} tx;
 	struct wait_event *subs;  /* recv wait_event the conn_stream associated is waiting on (via qc_subscribe) */
 	struct list list; /* To be used when adding in qcc->send_list or qcc->fctl_lsit */
diff --git a/src/h3.c b/src/h3.c
index 4acd95afe..a94b24b64 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -416,25 +416,15 @@ static int h3_control_send(struct h3_uqs *h3_uqs, void *ctx)
 	return ret;
 }
 
-/* Return next empty buffer of mux.
- * TODO to optimize memory consumption, a non-full buffer should be used before
- * allocating a new one.
- * TODO put this in mux ??
+/* Returns buffer for data sending.
+ * May be NULL if the allocation failed.
  */
-static struct buffer *get_mux_next_tx_buf(struct qcs *qcs)
+static struct buffer *mux_get_buf(struct qcs *qcs)
 {
-	struct buffer *buf = br_tail(qcs->tx.mbuf);
+	if (!b_size(&qcs->tx.buf))
+		b_alloc(&qcs->tx.buf);
 
-	if (b_data(buf))
-		buf = br_tail_add(qcs->tx.mbuf);
-
-	if (!b_size(buf))
-		qc_get_buf(qcs->qcc, buf);
-
-	if (!buf)
-		ABORT_NOW();
-
-	return buf;
+	return &qcs->tx.buf;
 }
 
 static int h3_resp_headers_send(struct qcs *qcs, struct htx *htx)
@@ -484,7 +474,7 @@ static int h3_resp_headers_send(struct qcs *qcs, struct htx *htx)
 
 	list[hdr].n = ist("");
 
-	res = get_mux_next_tx_buf(qcs);
+	res = mux_get_buf(qcs);
 
 	/* At least 5 bytes to store frame type + length as a varint max size */
 	if (b_room(res) < 5)
@@ -517,7 +507,6 @@ static int h3_resp_headers_send(struct qcs *qcs, struct htx *htx)
 	if (!b_quic_enc_int(res, b_data(&headers_buf)))
 		ABORT_NOW();
 	b_add(res, b_data(&headers_buf));
-	qcs->tx.left += 1 + frame_length_size + b_data(&headers_buf);
 
 	ret = 0;
 	blk = htx_get_head_blk(htx);
@@ -563,7 +552,7 @@ static int h3_resp_data_send(struct qcs *qcs, struct buffer *buf, size_t count)
 	if (type != HTX_BLK_DATA)
 		goto end;
 
-	res = get_mux_next_tx_buf(qcs);
+	res = mux_get_buf(qcs);
 
 	if (fsize > count)
 		fsize = count;
@@ -589,7 +578,6 @@ static int h3_resp_data_send(struct qcs *qcs, struct buffer *buf, size_t count)
 		htx_cut_data_blk(htx, blk, fsize);
 
 	b_add(res, b_data(&outbuf));
-	qcs->tx.left += b_data(&outbuf);
 	goto new_frame;
 
  end:
diff --git a/src/mux_quic.c b/src/mux_quic.c
index cb40e0b75..710aa0e63 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -905,6 +905,9 @@ static void qcs_destroy(struct qcs *qcs)
 		offer_buffers(NULL, 1);
 	}
 
+	b_free(&qcs->tx.buf);
+	b_free(&qcs->tx.xprt_buf);
+
 	if (qcs->subs)
 		qcs->subs->events = 0;
 
@@ -963,8 +966,7 @@ struct qcs *bidi_qcs_new(struct qcc *qcc, uint64_t id)
 	qcs->tx.acked_frms = EB_ROOT_UNIQUE;
 	qcs->tx.max_data = qcc->strms[qcs_type].tx.max_data;
 	qcs->tx.buf      = BUF_NULL;
-	br_init(qcs->tx.mbuf, sizeof(qcs->tx.mbuf) / sizeof(qcs->tx.mbuf[0]));
-	qcs->tx.left     = 0;
+	qcs->tx.xprt_buf = BUF_NULL;
 
 	eb64_insert(&qcc->streams_by_id, &qcs->by_id);
 	qcc->strms[qcs_type].nb_streams++;
@@ -1028,8 +1030,7 @@ struct qcs *luqs_new(struct qcc *qcc)
 	qcs->tx.offset     = qcs->tx.bytes = qcs->tx.ack_offset = 0;
 	qcs->tx.acked_frms = EB_ROOT_UNIQUE;
 	qcs->tx.buf        = BUF_NULL;
-	br_init(qcs->tx.mbuf, sizeof(qcs->tx.mbuf) / sizeof(qcs->tx.mbuf[0]));
-	qcs->tx.left = 0;
+	qcs->tx.xprt_buf   = BUF_NULL;
 
 	qcs->subs = NULL;
 	LIST_INIT(&qcs->list);
@@ -1070,8 +1071,8 @@ struct qcs *ruqs_new(struct qcc *qcc, uint64_t id)
 	qcs->rx.offset = qcs->rx.bytes = 0;
 	qcs->rx.buf = BUF_NULL;
 	qcs->rx.frms = EB_ROOT_UNIQUE;
-	br_init(qcs->tx.mbuf, sizeof(qcs->tx.mbuf) / sizeof(qcs->tx.mbuf[0]));
-	qcs->tx.left = 0;
+	qcs->tx.buf      = BUF_NULL;
+	qcs->tx.xprt_buf = BUF_NULL;
 
 	qcs->subs = NULL;
 	LIST_INIT(&qcs->list);
@@ -1304,7 +1305,7 @@ static int qc_recv(struct qcc *qcc)
 static int qcs_push_frame(struct qcs *qcs, struct buffer *payload, int fin, uint64_t offset)
 {
 	struct quic_frame *frm;
-	struct buffer *buf = &qcs->tx.buf;
+	struct buffer *buf = &qcs->tx.xprt_buf;
 	struct quic_enc_level *qel = &qcs->qcc->conn->qc->els[QUIC_TLS_ENC_LEVEL_APP];
 	int total = 0, to_xfer;
 
@@ -1348,7 +1349,6 @@ static int qcs_push_frame(struct qcs *qcs, struct buffer *payload, int fin, uint
  */
 static int qc_send(struct qcc *qcc)
 {
-	struct qcs *qcs;
 	struct eb64_node *node;
 	int ret, done;
 
@@ -1363,33 +1363,29 @@ static int qc_send(struct qcc *qcc)
 	 */
 	node = eb64_first(&qcc->streams_by_id);
 	while (node) {
-		struct buffer *buf;
-		qcs = container_of(node, struct qcs, by_id);
-		for (buf = br_head(qcs->tx.mbuf); b_size(buf); buf = br_del_head(qcs->tx.mbuf)) {
-			if (b_data(buf)) {
-				char fin = 0;
+		struct qcs *qcs = container_of(node, struct qcs, by_id);
+		struct buffer *buf = &qcs->tx.buf;
+		if (b_data(buf)) {
+			char fin = 0;
 
-				/* if FIN is activated, ensure the buffer to
-				 * send is the last
-				 */
-				if (qcs->flags & QC_SF_FIN_STREAM) {
-					BUG_ON(qcs->tx.left < b_data(buf));
-					fin = !(qcs->tx.left - b_data(buf));
-				}
-
-				ret = qcs_push_frame(qcs, buf, fin, qcs->tx.offset);
-				if (ret < 0)
-					ABORT_NOW();
-
-				qcs->tx.left -= ret;
-				qcs->tx.offset += ret;
-				if (b_data(buf)) {
-					qcc->conn->xprt->subscribe(qcc->conn, qcc->conn->xprt_ctx,
-											   SUB_RETRY_SEND, &qcc->wait_event);
-					break;
-				}
+			/* if FIN is activated, ensure the buffer to
+			 * send is the last
+			 */
+			if (qcs->flags & QC_SF_FIN_STREAM) {
+				BUG_ON(b_data(&qcs->tx.buf) < b_data(buf));
+				fin = (b_data(&qcs->tx.buf) - b_data(buf) == 0);
+			}
+
+			ret = qcs_push_frame(qcs, buf, fin, qcs->tx.offset);
+			if (ret < 0)
+				ABORT_NOW();
+
+			qcs->tx.offset += ret;
+			if (b_data(buf)) {
+				qcc->conn->xprt->subscribe(qcc->conn, qcc->conn->xprt_ctx,
+				                           SUB_RETRY_SEND, &qcc->wait_event);
+				break;
 			}
-			b_free(buf);
 		}
 		node = eb64_next(node);
 	}