diff --git a/include/haproxy/mux_quic-t.h b/include/haproxy/mux_quic-t.h
index 22fd1b910..de68a40ff 100644
--- a/include/haproxy/mux_quic-t.h
+++ b/include/haproxy/mux_quic-t.h
@@ -68,6 +68,7 @@ struct qcc {
 	struct {
 		struct quic_fctl fc; /* stream flow control applied on sending */
 		int avail_bufs; /* count of available buffers for this connection */
+		uint64_t buf_in_flight; /* sum of currently allocated Tx buffer sizes */
 	} tx;
 
 	uint64_t largest_bidi_r; /* largest remote bidi stream ID opened. */
diff --git a/include/haproxy/mux_quic.h b/include/haproxy/mux_quic.h
index c61044760..f1ed218a5 100644
--- a/include/haproxy/mux_quic.h
+++ b/include/haproxy/mux_quic.h
@@ -23,7 +23,7 @@ int qcs_is_close_remote(struct qcs *qcs);
 int qcs_subscribe(struct qcs *qcs, int event_type, struct wait_event *es);
 void qcs_notify_recv(struct qcs *qcs);
 void qcs_notify_send(struct qcs *qcs);
-void qcc_notify_buf(struct qcc *qcc, int free_count);
+void qcc_notify_buf(struct qcc *qcc, int free_count, uint64_t free_size);
 
 struct buffer *qcc_get_stream_rxbuf(struct qcs *qcs);
 struct buffer *qcc_get_stream_txbuf(struct qcs *qcs, int *err);
diff --git a/src/mux_quic.c b/src/mux_quic.c
index dd315d078..d30ca2976 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -524,10 +524,10 @@ void qcs_notify_send(struct qcs *qcs)
 	}
 }
 
-/* Report that <free_count> stream-desc buffer have been released for <qcc>
- * connection.
+/* Report that one or several stream-desc buffers have been released for <qcc>
+ * connection. <free_size> represent the sum of freed buffers sizes.
  */
-void qcc_notify_buf(struct qcc *qcc, int free_count)
+void qcc_notify_buf(struct qcc *qcc, int free_count, uint64_t free_size)
 {
 	struct qcs *qcs;
 
@@ -536,6 +536,10 @@ void qcc_notify_buf(struct qcc *qcc, int free_count)
 	BUG_ON(qcc->tx.avail_bufs + free_count > global.tune.quic_streams_buf);
 	qcc->tx.avail_bufs += free_count;
 
+	/* Cannot have a negative buf_in_flight counter */
+	BUG_ON(qcc->tx.buf_in_flight < free_size);
+	qcc->tx.buf_in_flight -= free_size;
+
 	if (qcc->flags & QC_CF_CONN_FULL) {
 		TRACE_STATE("new stream desc buffer available", QMUX_EV_QCC_WAKE, qcc->conn);
 		qcc->flags &= ~QC_CF_CONN_FULL;
@@ -1059,8 +1063,10 @@ struct buffer *qcc_get_stream_txbuf(struct qcs *qcs, int *err)
 			goto out;
 		}
 
-		if (likely(!unlimited))
+		if (likely(!unlimited)) {
 			--qcc->tx.avail_bufs;
+			qcc->tx.buf_in_flight += global.tune.bufsize;
+		}
 	}
 
  out:
@@ -2728,6 +2734,7 @@ static int qmux_init(struct connection *conn, struct proxy *prx,
 	qcc->rfctl.msd_uni_l = rparams->initial_max_stream_data_uni;
 
 	qcc->tx.avail_bufs = global.tune.quic_streams_buf;
+	qcc->tx.buf_in_flight = 0;
 
 	if (conn_is_back(conn)) {
 		qcc->next_bidi_l    = 0x00;
diff --git a/src/quic_stream.c b/src/quic_stream.c
index a0baa0b98..c99266978 100644
--- a/src/quic_stream.c
+++ b/src/quic_stream.c
@@ -28,6 +28,7 @@ static void qc_stream_buf_free(struct qc_stream_desc *stream,
 {
 	struct quic_conn *qc = stream->qc;
 	struct buffer *buf = &(*stream_buf)->buf;
+	uint64_t free_size;
 
 	LIST_DEL_INIT(&(*stream_buf)->list);
 
@@ -35,6 +36,7 @@ static void qc_stream_buf_free(struct qc_stream_desc *stream,
 	if (*stream_buf == stream->buf)
 		stream->buf = NULL;
 
+	free_size = b_size(buf);
 	b_free(buf);
 	offer_buffers(NULL, 1);
 	pool_free(pool_head_quic_stream_buf, *stream_buf);
@@ -44,7 +46,7 @@ static void qc_stream_buf_free(struct qc_stream_desc *stream,
 	if (qc->mux_state == QC_MUX_READY) {
 		if (!(stream->flags & QC_SD_FL_OOB_BUF)) {
 			/* notify MUX about available buffers. */
-			qcc_notify_buf(qc->qcc, 1);
+			qcc_notify_buf(qc->qcc, 1, free_size);
 		}
 	}
 }
@@ -200,6 +202,7 @@ void qc_stream_desc_free(struct qc_stream_desc *stream, int closing)
 	struct quic_conn *qc = stream->qc;
 	struct eb64_node *frm_node;
 	unsigned int free_count = 0;
+	uint64_t free_size = 0;
 
 	/* This function only deals with released streams. */
 	BUG_ON(!(stream->flags & QC_SD_FL_RELEASE));
@@ -207,6 +210,7 @@ void qc_stream_desc_free(struct qc_stream_desc *stream, int closing)
 	/* free remaining stream buffers */
 	list_for_each_entry_safe(buf, buf_back, &stream->buf_list, list) {
 		if (!(b_data(&buf->buf)) || closing) {
+			free_size += b_size(&buf->buf);
 			b_free(&buf->buf);
 			LIST_DELETE(&buf->list);
 			pool_free(pool_head_quic_stream_buf, buf);
@@ -220,7 +224,7 @@ void qc_stream_desc_free(struct qc_stream_desc *stream, int closing)
 		if (qc->mux_state == QC_MUX_READY) {
 			if (!(stream->flags & QC_SD_FL_OOB_BUF)) {
 				/* notify MUX about available buffers. */
-				qcc_notify_buf(qc->qcc, free_count);
+				qcc_notify_buf(qc->qcc, free_count, free_size);
 			}
 		}
 	}