diff --git a/include/haproxy/mux_quic-t.h b/include/haproxy/mux_quic-t.h
index 3bded6753..1515a5bc5 100644
--- a/include/haproxy/mux_quic-t.h
+++ b/include/haproxy/mux_quic-t.h
@@ -55,6 +55,7 @@ struct qcc {
 
 #define QC_SF_NONE              0x00000000
 #define QC_SF_FIN_STREAM        0x00000001  // FIN bit must be set for last frame of the stream
+#define QC_SF_BLK_MROOM         0x00000002  // app layer is blocked waiting for room in the qcs.tx.buf
 
 struct qcs {
 	struct qcc *qcc;
diff --git a/src/h3.c b/src/h3.c
index 359b27676..0ed180027 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -534,11 +534,14 @@ static int h3_resp_data_send(struct qcs *qcs, struct buffer *buf, size_t count)
 		b_slow_realign(res, trash.area, b_data(res));
 	}
 
-	/* not enough room for headers and at least one data byte, block the
-	 * stream
+	/* Not enough room for headers and at least one data byte, block the
+	 * stream. It is expected that the conn-stream layer will subscribe on
+	 * SEND.
 	 */
-	if (b_size(&outbuf) <= hsize)
-		ABORT_NOW();
+	if (b_size(&outbuf) <= hsize) {
+		qcs->flags |= QC_SF_BLK_MROOM;
+		goto end;
+	}
 
 	if (b_size(&outbuf) < hsize + fsize)
 		fsize = b_size(&outbuf) - hsize;
@@ -579,7 +582,7 @@ size_t h3_snd_buf(struct conn_stream *cs, struct buffer *buf, size_t count, int
 
 	htx = htx_from_buf(buf);
 
-	while (count && !htx_is_empty(htx)) {
+	while (count && !htx_is_empty(htx) && !(qcs->flags & QC_SF_BLK_MROOM)) {
 		idx = htx_get_head(htx);
 		blk = htx_get_blk(htx, idx);
 		btype = htx_get_blk_type(blk);
diff --git a/src/hq_interop.c b/src/hq_interop.c
index 3d530f4bf..075e785b0 100644
--- a/src/hq_interop.c
+++ b/src/hq_interop.c
@@ -81,7 +81,7 @@ static size_t hq_interop_snd_buf(struct conn_stream *cs, struct buffer *buf,
 	res = mux_get_buf(qcs);
 	outbuf = b_make(b_tail(res), b_contig_space(res), 0, 0);
 
-	while (count && !htx_is_empty(htx)) {
+	while (count && !htx_is_empty(htx) && !(qcs->flags & QC_SF_BLK_MROOM)) {
 		/* Not implemented : QUIC on backend side */
 		idx = htx_get_head(htx);
 		blk = htx_get_blk(htx, idx);
diff --git a/src/mux_quic.c b/src/mux_quic.c
index c11e1cedd..2a28a5155 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -193,6 +193,9 @@ static int qc_send(struct qcc *qcc)
 
 			if (ret > 0) {
 				qcs_notify_send(qcs);
+				if (qcs->flags & QC_SF_BLK_MROOM)
+					qcs->flags &= ~QC_SF_BLK_MROOM;
+
 				xprt_wake = 1;
 			}