diff --git a/src/mux_h1.c b/src/mux_h1.c
index 6f6b95e06..96701d614 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -4450,7 +4450,7 @@ static size_t h1_nego_ff(struct stconn *sc, struct buffer *input, size_t count,
 	struct h1s *h1s = __sc_mux_strm(sc);
 	struct h1c *h1c = h1s->h1c;
 	struct h1m *h1m = (!(h1c->flags & H1C_F_IS_BACK) ? &h1s->res : &h1s->req);
-	size_t ret = 0;
+	size_t sz, offset = 0, ret = 0;
 
 	TRACE_ENTER(H1_EV_STRM_SEND, h1c->conn, h1s, 0, (size_t[]){count});
 
@@ -4487,9 +4487,18 @@ static size_t h1_nego_ff(struct stconn *sc, struct buffer *input, size_t count,
 				h1m->curr_len = count;
 			}
 			else {
-				/* XXX: Unsupported for now but will be added soon ! */
-				h1s->sd->iobuf.flags |= IOBUF_FL_NO_FF;
-				goto out;
+				/* The producer does not know the chunk size, thus this will be emitted at the
+				 * end, in done_ff(). So splicing cannot be used (see TODO below).
+				 * We will reserve 12 bytes to handle at most 4Go chunk with all CRLFs !
+				 * (<8-bytes SIZE><CRLF><CHUNK-DATA><CRLF>)
+				 */
+				if (count > MAX_RANGE(unsigned int))
+					count = MAX_RANGE(unsigned int);
+				offset = 12;
+				/* Add 2 more bytes to finish the previous chunk */
+				if (h1m->state == H1_MSG_CHUNK_CRLF)
+					offset += 2;
+				goto no_splicing;
 			}
 		}
 	}
@@ -4514,6 +4523,7 @@ static size_t h1_nego_ff(struct stconn *sc, struct buffer *input, size_t count,
 		TRACE_DEVEL("Unable to allocate pipe for splicing, fallback to buffer", H1_EV_STRM_SEND, h1c->conn, h1s);
 	}
 
+  no_splicing:
 	if (!h1_get_buf(h1c, &h1c->obuf)) {
 		h1c->flags |= H1C_F_OUT_ALLOC;
 		TRACE_STATE("waiting for opposite h1c obuf allocation", H1_EV_STRM_SEND|H1_EV_H1S_BLK, h1c->conn, h1s);
@@ -4523,13 +4533,11 @@ static size_t h1_nego_ff(struct stconn *sc, struct buffer *input, size_t count,
 	if (b_space_wraps(&h1c->obuf))
 		b_slow_realign(&h1c->obuf, trash.area, b_data(&h1c->obuf));
 
-	h1s->sd->iobuf.buf = &h1c->obuf;
-	h1s->sd->iobuf.offset = 0;
-	h1s->sd->iobuf.data = 0;
 
 	/* Cannot forward more than available room in output buffer */
-	if (count > b_room(&h1c->obuf))
-		count = b_room(&h1c->obuf);
+	sz = b_contig_space(&h1c->obuf) - offset;
+	if (count > sz)
+		count = sz;
 
 	if (!count) {
 		h1c->flags |= H1C_F_OUT_FULL;
@@ -4538,6 +4546,10 @@ static size_t h1_nego_ff(struct stconn *sc, struct buffer *input, size_t count,
 		goto out;
 	}
 
+	h1s->sd->iobuf.buf = &h1c->obuf;
+	h1s->sd->iobuf.offset = offset;
+	h1s->sd->iobuf.data = 0;
+
 	/* forward remaining input data */
 	if (b_data(input)) {
 		size_t xfer = count;
@@ -4584,6 +4596,16 @@ static size_t h1_done_ff(struct stconn *sc)
 		if (b_room(&h1c->obuf) == sd->iobuf.offset)
 			h1c->flags |= H1C_F_OUT_FULL;
 
+		if (sd->iobuf.offset) {
+			b_add(&h1c->obuf, sd->iobuf.offset);
+			b_del(&h1c->obuf, sd->iobuf.offset);
+			h1_prepend_chunk_size(&h1c->obuf, sd->iobuf.data, sd->iobuf.offset - ((h1m->state == H1_MSG_CHUNK_CRLF) ?  4 : 2));
+			h1_append_chunk_crlf(&h1c->obuf);
+			if (h1m->state == H1_MSG_CHUNK_CRLF)
+				h1_prepend_chunk_crlf(&h1c->obuf);
+			h1m->state = H1_MSG_CHUNK_SIZE;
+		}
+
 		total = sd->iobuf.data;
 		sd->iobuf.buf = NULL;
 		sd->iobuf.offset = 0;