diff --git a/src/mux_h2.c b/src/mux_h2.c
index b81d79970..ce39f750b 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -1666,6 +1666,7 @@ static int h2c_frt_recv_preface(struct h2c *h2c)
 			sess_log(h2c->conn->owner);
 
 		if (ret1 < 0 || conn_xprt_read0_pending(h2c->conn)) {
+			TRACE_ERROR("I/O error or short read", H2_EV_RX_FRAME|H2_EV_RX_PREFACE, h2c->conn);
 			h2c_error(h2c, H2_ERR_PROTOCOL_ERROR);
 			HA_ATOMIC_ADD(&h2c->px_counters->conn_proto_err, 1);
 		}
@@ -2148,6 +2149,7 @@ static int h2c_handle_settings(struct h2c *h2c)
 			break;
 		case H2_SETTINGS_MAX_FRAME_SIZE:
 			if (arg < 16384 || arg > 16777215) { // RFC7540#6.5.2
+				TRACE_ERROR("MAX_FRAME_SIZE out of range", H2_EV_RX_FRAME|H2_EV_RX_SETTINGS, h2c->conn);
 				error = H2_ERR_PROTOCOL_ERROR;
 				HA_ATOMIC_ADD(&h2c->px_counters->conn_proto_err, 1);
 				goto fail;
@@ -2156,6 +2158,7 @@ static int h2c_handle_settings(struct h2c *h2c)
 			break;
 		case H2_SETTINGS_ENABLE_PUSH:
 			if (arg < 0 || arg > 1) { // RFC7540#6.5.2
+				TRACE_ERROR("ENABLE_PUSH out of range", H2_EV_RX_FRAME|H2_EV_RX_SETTINGS, h2c->conn);
 				error = H2_ERR_PROTOCOL_ERROR;
 				HA_ATOMIC_ADD(&h2c->px_counters->conn_proto_err, 1);
 				goto fail;
@@ -2426,12 +2429,14 @@ static int h2c_handle_window_update(struct h2c *h2c, struct h2s *h2s)
 			goto done;
 
 		if (!inc) {
+			TRACE_ERROR("stream WINDOW_UPDATE inc=0", H2_EV_RX_FRAME|H2_EV_RX_WU, h2c->conn, h2s);
 			error = H2_ERR_PROTOCOL_ERROR;
 			HA_ATOMIC_ADD(&h2c->px_counters->strm_proto_err, 1);
 			goto strm_err;
 		}
 
 		if (h2s_mws(h2s) >= 0 && h2s_mws(h2s) + inc < 0) {
+			TRACE_ERROR("stream WINDOW_UPDATE inc<0", H2_EV_RX_FRAME|H2_EV_RX_WU, h2c->conn, h2s);
 			error = H2_ERR_FLOW_CONTROL_ERROR;
 			HA_ATOMIC_ADD(&h2c->px_counters->strm_proto_err, 1);
 			goto strm_err;
@@ -2449,6 +2454,7 @@ static int h2c_handle_window_update(struct h2c *h2c, struct h2s *h2s)
 	else {
 		/* connection window update */
 		if (!inc) {
+			TRACE_ERROR("conn WINDOW_UPDATE inc=0", H2_EV_RX_FRAME|H2_EV_RX_WU, h2c->conn);
 			error = H2_ERR_PROTOCOL_ERROR;
 			HA_ATOMIC_ADD(&h2c->px_counters->conn_proto_err, 1);
 			goto conn_err;
@@ -2521,6 +2527,7 @@ static int h2c_handle_priority(struct h2c *h2c)
 
 	if (h2_get_n32(&h2c->dbuf, 0) == h2c->dsi) {
 		/* 7540#5.3 : can't depend on itself */
+		TRACE_ERROR("PRIORITY depends on itself", H2_EV_RX_FRAME|H2_EV_RX_WU, h2c->conn);
 		h2c_error(h2c, H2_ERR_PROTOCOL_ERROR);
 		HA_ATOMIC_ADD(&h2c->px_counters->conn_proto_err, 1);
 		TRACE_DEVEL("leaving on error", H2_EV_RX_FRAME|H2_EV_RX_PRIO, h2c->conn);
@@ -2617,6 +2624,7 @@ static struct h2s *h2c_frt_handle_headers(struct h2c *h2c, struct h2s *h2s)
 	else if (h2c->dsi <= h2c->max_id || !(h2c->dsi & 1)) {
 		/* RFC7540#5.1.1 stream id > prev ones, and must be odd here */
 		error = H2_ERR_PROTOCOL_ERROR;
+		TRACE_ERROR("HEADERS on invalid stream ID", H2_EV_RX_FRAME|H2_EV_RX_HDR, h2c->conn);
 		HA_ATOMIC_ADD(&h2c->px_counters->conn_proto_err, 1);
 		sess_log(h2c->conn->owner);
 		goto conn_err;
@@ -2735,6 +2743,7 @@ static struct h2s *h2c_bck_handle_headers(struct h2c *h2c, struct h2s *h2s)
 
 	if (h2s->st != H2_SS_OPEN && h2s->st != H2_SS_HLOC) {
 		/* RFC7540#5.1 */
+		TRACE_ERROR("response HEADERS in invalid state", H2_EV_RX_FRAME|H2_EV_RX_HDR, h2c->conn, h2s);
 		h2s_error(h2s, H2_ERR_STREAM_CLOSED);
 		h2c->st0 = H2_CS_FRAME_E;
 		HA_ATOMIC_ADD(&h2c->px_counters->strm_proto_err, 1);
@@ -2746,6 +2755,7 @@ static struct h2s *h2c_bck_handle_headers(struct h2c *h2c, struct h2s *h2s)
 			goto fail; // missing data
 
 		/* stream error : send RST_STREAM */
+		TRACE_ERROR("couldn't decode response HEADERS", H2_EV_RX_FRAME|H2_EV_RX_HDR, h2c->conn, h2s);
 		h2s_error(h2s, H2_ERR_PROTOCOL_ERROR);
 		h2c->st0 = H2_CS_FRAME_E;
 		HA_ATOMIC_ADD(&h2c->px_counters->strm_proto_err, 1);
@@ -2813,6 +2823,7 @@ static int h2c_frt_handle_data(struct h2c *h2c, struct h2s *h2s)
 
 	if ((h2s->flags & H2_SF_DATA_CLEN) && (h2c->dfl - h2c->dpl) > h2s->body_len) {
 		/* RFC7540#8.1.2 */
+		TRACE_ERROR("DATA frame larger than content-length", H2_EV_RX_FRAME|H2_EV_RX_DATA, h2c->conn, h2s);
 		error = H2_ERR_PROTOCOL_ERROR;
 		HA_ATOMIC_ADD(&h2c->px_counters->strm_proto_err, 1);
 		goto strm_err;
@@ -2857,6 +2868,7 @@ static int h2c_frt_handle_data(struct h2c *h2c, struct h2s *h2s)
 
 		if (h2s->flags & H2_SF_DATA_CLEN && h2s->body_len) {
 			/* RFC7540#8.1.2 */
+			TRACE_ERROR("ES on DATA frame before content-length", H2_EV_RX_FRAME|H2_EV_RX_DATA, h2c->conn, h2s);
 			error = H2_ERR_PROTOCOL_ERROR;
 			HA_ATOMIC_ADD(&h2c->px_counters->strm_proto_err, 1);
 			goto strm_err;
@@ -2889,6 +2901,7 @@ static int h2_frame_check_vs_state(struct h2c *h2c, struct h2s *h2s)
 		/* RFC7540#5.1: any frame other than HEADERS or PRIORITY in
 		 * this state MUST be treated as a connection error
 		 */
+		TRACE_ERROR("invalid frame type for IDLE state", H2_EV_RX_FRAME|H2_EV_RX_FHDR, h2c->conn, h2s);
 		h2c_error(h2c, H2_ERR_PROTOCOL_ERROR);
 		if (!h2c->nb_streams && !(h2c->flags & H2_CF_IS_BACK)) {
 			/* only log if no other stream can report the error */
@@ -2901,6 +2914,7 @@ static int h2_frame_check_vs_state(struct h2c *h2c, struct h2s *h2s)
 
 	if (h2s->st == H2_SS_IDLE && (h2c->flags & H2_CF_IS_BACK)) {
 		/* only PUSH_PROMISE would be permitted here */
+		TRACE_ERROR("invalid frame type for IDLE state (back)", H2_EV_RX_FRAME|H2_EV_RX_FHDR, h2c->conn, h2s);
 		h2c_error(h2c, H2_ERR_PROTOCOL_ERROR);
 		HA_ATOMIC_ADD(&h2c->px_counters->conn_proto_err, 1);
 		TRACE_DEVEL("leaving in error (idle&back)", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn, h2s);
@@ -2915,6 +2929,7 @@ static int h2_frame_check_vs_state(struct h2c *h2c, struct h2s *h2s)
 		 * PUSH_PROMISE/CONTINUATION cause connection errors.
 		 */
 		if (h2_ft_bit(h2c->dft) & H2_FT_HDR_MASK) {
+			TRACE_ERROR("invalid frame type for HREM state", H2_EV_RX_FRAME|H2_EV_RX_FHDR, h2c->conn, h2s);
 			h2c_error(h2c, H2_ERR_PROTOCOL_ERROR);
 			HA_ATOMIC_ADD(&h2c->px_counters->conn_proto_err, 1);
 		}
@@ -3051,7 +3066,7 @@ static void h2_process_demux(struct h2c *h2c)
 			if (!h2_get_frame_hdr(&h2c->dbuf, &hdr)) {
 				/* RFC7540#3.5: a GOAWAY frame MAY be omitted */
 				if (h2c->st0 == H2_CS_ERROR) {
-					TRACE_PROTO("failed to receive settings", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_RX_SETTINGS|H2_EV_PROTO_ERR, h2c->conn);
+					TRACE_ERROR("failed to receive settings", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_RX_SETTINGS|H2_EV_PROTO_ERR, h2c->conn);
 					h2c->st0 = H2_CS_ERROR2;
 					if (!(h2c->flags & H2_CF_IS_BACK))
 						sess_log(h2c->conn->owner);
@@ -3061,7 +3076,7 @@ static void h2_process_demux(struct h2c *h2c)
 
 			if (hdr.sid || hdr.ft != H2_FT_SETTINGS || hdr.ff & H2_F_SETTINGS_ACK) {
 				/* RFC7540#3.5: a GOAWAY frame MAY be omitted */
-				TRACE_PROTO("unexpected frame type or flags", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_RX_SETTINGS|H2_EV_PROTO_ERR, h2c->conn);
+				TRACE_ERROR("unexpected frame type or flags", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_RX_SETTINGS|H2_EV_PROTO_ERR, h2c->conn);
 				h2c_error(h2c, H2_ERR_PROTOCOL_ERROR);
 				h2c->st0 = H2_CS_ERROR2;
 				if (!(h2c->flags & H2_CF_IS_BACK))
@@ -3072,7 +3087,7 @@ static void h2_process_demux(struct h2c *h2c)
 
 			if ((int)hdr.len < 0 || (int)hdr.len > global.tune.bufsize) {
 				/* RFC7540#3.5: a GOAWAY frame MAY be omitted */
-				TRACE_PROTO("invalid settings frame length", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_RX_SETTINGS|H2_EV_PROTO_ERR, h2c->conn);
+				TRACE_ERROR("invalid settings frame length", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_RX_SETTINGS|H2_EV_PROTO_ERR, h2c->conn);
 				h2c_error(h2c, H2_ERR_FRAME_SIZE_ERROR);
 				h2c->st0 = H2_CS_ERROR2;
 				if (!(h2c->flags & H2_CF_IS_BACK))
@@ -3112,7 +3127,7 @@ static void h2_process_demux(struct h2c *h2c)
 				break;
 
 			if ((int)hdr.len < 0 || (int)hdr.len > global.tune.bufsize) {
-				TRACE_PROTO("invalid H2 frame length", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn);
+				TRACE_ERROR("invalid H2 frame length", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn);
 				h2c_error(h2c, H2_ERR_FRAME_SIZE_ERROR);
 				if (!h2c->nb_streams && !(h2c->flags & H2_CF_IS_BACK)) {
 					/* only log if no other stream can report the error */
@@ -3132,7 +3147,7 @@ static void h2_process_demux(struct h2c *h2c)
 				 * padlen in the flow control, so it must be adjusted.
 				 */
 				if (hdr.len < 1) {
-					TRACE_PROTO("invalid H2 padded frame length", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn);
+					TRACE_ERROR("invalid H2 padded frame length", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn);
 					h2c_error(h2c, H2_ERR_FRAME_SIZE_ERROR);
 					if (!(h2c->flags & H2_CF_IS_BACK))
 						sess_log(h2c->conn->owner);
@@ -3147,7 +3162,7 @@ static void h2_process_demux(struct h2c *h2c)
 				padlen = *(uint8_t *)b_peek(&h2c->dbuf, 9);
 
 				if (padlen > hdr.len) {
-					TRACE_PROTO("invalid H2 padding length", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn);
+					TRACE_ERROR("invalid H2 padding length", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn);
 					/* RFC7540#6.1 : pad length = length of
 					 * frame payload or greater => error.
 					 */
@@ -3178,7 +3193,7 @@ static void h2_process_demux(struct h2c *h2c)
 			/* check for minimum basic frame format validity */
 			ret = h2_frame_check(h2c->dft, 1, h2c->dsi, h2c->dfl, global.tune.bufsize);
 			if (ret != H2_ERR_NO_ERROR) {
-				TRACE_PROTO("received invalid H2 frame header", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn);
+				TRACE_ERROR("received invalid H2 frame header", H2_EV_RX_FRAME|H2_EV_RX_FHDR|H2_EV_PROTO_ERR, h2c->conn);
 				h2c_error(h2c, ret);
 				if (!(h2c->flags & H2_CF_IS_BACK))
 					sess_log(h2c->conn->owner);
@@ -3254,7 +3269,7 @@ static void h2_process_demux(struct h2c *h2c)
 			 * frames' parsers consume all following CONTINUATION
 			 * frames so this one is out of sequence.
 			 */
-			TRACE_PROTO("received unexpected H2 CONTINUATION frame", H2_EV_RX_FRAME|H2_EV_RX_CONT|H2_EV_H2C_ERR, h2c->conn, h2s);
+			TRACE_ERROR("received unexpected H2 CONTINUATION frame", H2_EV_RX_FRAME|H2_EV_RX_CONT|H2_EV_H2C_ERR, h2c->conn, h2s);
 			h2c_error(h2c, H2_ERR_PROTOCOL_ERROR);
 			if (!(h2c->flags & H2_CF_IS_BACK))
 				sess_log(h2c->conn->owner);
@@ -4834,7 +4849,7 @@ static size_t h2s_frt_make_resp_headers(struct h2s *h2s, struct htx *htx)
 	sl = htx_get_blk_ptr(htx, blk);
 	h2s->status = sl->info.res.status;
 	if (h2s->status < 100 || h2s->status > 999) {
-		TRACE_PROTO("will not encode an invalid status code", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
+		TRACE_ERROR("will not encode an invalid status code", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
 		goto fail;
 	}
 
@@ -4853,7 +4868,7 @@ static size_t h2s_frt_make_resp_headers(struct h2s *h2s, struct htx *htx)
 			break;
 
 		if (unlikely(hdr >= sizeof(list)/sizeof(list[0]) - 1)) {
-			TRACE_PROTO("too many headers", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
+			TRACE_ERROR("too many headers", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
 			goto fail;
 		}
 
@@ -5070,7 +5085,7 @@ static size_t h2s_bck_make_req_headers(struct h2s *h2s, struct htx *htx)
 	meth = htx_sl_req_meth(sl);
 	uri  = htx_sl_req_uri(sl);
 	if (unlikely(uri.len == 0)) {
-		TRACE_PROTO("no URI in HTX request", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
+		TRACE_ERROR("no URI in HTX request", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
 		goto fail;
 	}
 
@@ -5089,7 +5104,7 @@ static size_t h2s_bck_make_req_headers(struct h2s *h2s, struct htx *htx)
 			break;
 
 		if (unlikely(hdr >= sizeof(list)/sizeof(list[0]) - 1)) {
-			TRACE_PROTO("too many headers", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
+			TRACE_ERROR("too many headers", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
 			goto fail;
 		}
 
@@ -5707,7 +5722,7 @@ static size_t h2s_make_trailers(struct h2s *h2s, struct htx *htx)
 			break;
 
 		if (unlikely(hdr >= sizeof(list)/sizeof(list[0]) - 1)) {
-			TRACE_PROTO("too many headers", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
+			TRACE_ERROR("too many trailers", H2_EV_TX_FRAME|H2_EV_TX_HDR|H2_EV_H2S_ERR, h2c->conn, h2s);
 			goto fail;
 		}