diff --git a/astlpc.c b/astlpc.c
index 5218c92..616ed1d 100644
--- a/astlpc.c
+++ b/astlpc.c
@@ -178,12 +178,12 @@
 		return;
 	}
 
-	if (len > MCTP_MTU + sizeof(struct mctp_hdr)) {
+	if (len > astlpc->binding.pkt_size) {
 		mctp_prwarn("invalid RX len 0x%x", len);
 		return;
 	}
 
-	pkt = mctp_pktbuf_alloc(len);
+	pkt = mctp_pktbuf_alloc(&astlpc->binding, len);
 	if (!pkt)
 		goto out_complete;
 
@@ -335,6 +335,8 @@
 	astlpc->binding.name = "astlpc";
 	astlpc->binding.version = 1;
 	astlpc->binding.tx = mctp_binding_astlpc_tx;
+	astlpc->binding.pkt_size = MCTP_BMTU;
+	astlpc->binding.pkt_pad = 0;
 
 	rc = mctp_astlpc_init_lpc(astlpc);
 	if (rc) {
diff --git a/core.c b/core.c
index 2a9784e..ff4bd63 100644
--- a/core.c
+++ b/core.c
@@ -60,16 +60,18 @@
 #define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
 #endif
 
-struct mctp_pktbuf *mctp_pktbuf_alloc(uint8_t len)
+struct mctp_pktbuf *mctp_pktbuf_alloc(struct mctp_binding *binding, size_t len)
 {
 	struct mctp_pktbuf *buf;
+	size_t size;
 
-	BUILD_ASSERT(MCTP_PKTBUF_SIZE <= 0xff);
+	size = binding->pkt_size + binding->pkt_pad;
 
 	/* todo: pools */
-	buf = __mctp_alloc(sizeof(*buf));
+	buf = __mctp_alloc(sizeof(*buf) + size);
 
-	buf->start = MCTP_PKTBUF_BINDING_PAD;
+	buf->size = size;
+	buf->start = binding->pkt_pad;
 	buf->end = buf->start + len;
 	buf->mctp_hdr_off = buf->start;
 	buf->next = NULL;
@@ -97,30 +99,28 @@
 	return pkt->end - pkt->start;
 }
 
-void *mctp_pktbuf_alloc_start(struct mctp_pktbuf *pkt, uint8_t size)
+void *mctp_pktbuf_alloc_start(struct mctp_pktbuf *pkt, size_t size)
 {
 	assert(size <= pkt->start);
 	pkt->start -= size;
 	return pkt->data + pkt->start;
 }
 
-void *mctp_pktbuf_alloc_end(struct mctp_pktbuf *pkt, uint8_t size)
+void *mctp_pktbuf_alloc_end(struct mctp_pktbuf *pkt, size_t size)
 {
 	void *buf;
 
-	assert(size < (MCTP_PKTBUF_SIZE - pkt->end));
+	assert(size < (pkt->size - pkt->end));
 	buf = pkt->data + pkt->end;
 	pkt->end += size;
 	return buf;
 }
 
-int mctp_pktbuf_push(struct mctp_pktbuf *pkt, void *data, uint8_t len)
+int mctp_pktbuf_push(struct mctp_pktbuf *pkt, void *data, size_t len)
 {
 	void *p;
 
-	assert(pkt->end + len <= MCTP_PKTBUF_SIZE);
-
-	if (pkt->end + len > MCTP_PKTBUF_SIZE)
+	if (pkt->end + len > pkt->size)
 		return -1;
 
 	p = pkt->data + pkt->end;
@@ -355,9 +355,6 @@
 	if (!bus->tx_enabled)
 		return -1;
 
-	mctp_prdebug("sending pkt, len %d",
-			mctp_pktbuf_size(pkt));
-
 	return bus->binding->tx(bus->binding, pkt);
 }
 
@@ -392,21 +389,22 @@
 int mctp_message_tx(struct mctp *mctp, mctp_eid_t eid,
 		void *msg, size_t msg_len)
 {
+	size_t max_payload_len, payload_len, p;
 	struct mctp_pktbuf *pkt;
 	struct mctp_hdr *hdr;
 	struct mctp_bus *bus;
-	size_t pkt_len, p;
 	int i;
 
 	bus = find_bus_for_eid(mctp, eid);
+	max_payload_len = bus->binding->pkt_size - sizeof(*hdr);
 
 	/* queue up packets, each of max MCTP_MTU size */
 	for (p = 0, i = 0; p < msg_len; i++) {
-		pkt_len = msg_len - p;
-		if (pkt_len > MCTP_MTU)
-			pkt_len = MCTP_MTU;
+		payload_len = msg_len - p;
+		if (payload_len > max_payload_len)
+			payload_len = max_payload_len;
 
-		pkt = mctp_pktbuf_alloc(pkt_len + sizeof(*hdr));
+		pkt = mctp_pktbuf_alloc(bus->binding, payload_len + sizeof(*hdr));
 		hdr = mctp_pktbuf_hdr(pkt);
 
 		/* todo: tags */
@@ -418,12 +416,12 @@
 
 		if (i == 0)
 			hdr->flags_seq_tag |= MCTP_HDR_FLAG_SOM;
-		if (p + pkt_len >= msg_len)
+		if (p + payload_len >= msg_len)
 			hdr->flags_seq_tag |= MCTP_HDR_FLAG_EOM;
 		hdr->flags_seq_tag |=
 			(i & MCTP_HDR_SEQ_MASK) << MCTP_HDR_SEQ_SHIFT;
 
-		memcpy(mctp_pktbuf_data(pkt), msg + p, pkt_len);
+		memcpy(mctp_pktbuf_data(pkt), msg + p, payload_len);
 
 		/* add to tx queue */
 		if (bus->tx_queue_tail)
@@ -432,7 +430,7 @@
 			bus->tx_queue_head = pkt;
 		bus->tx_queue_tail = pkt;
 
-		p += pkt_len;
+		p += payload_len;
 	}
 
 	mctp_send_tx_queue(bus);
diff --git a/libmctp.h b/libmctp.h
index ecf78c6..5219a35 100644
--- a/libmctp.h
+++ b/libmctp.h
@@ -31,41 +31,33 @@
 #define MCTP_HDR_TAG_SHIFT	(0)
 #define MCTP_HDR_TAG_MASK	(0x7)
 
-/* Maximum size of *payload* data in a MCTP packet
- * @todo: dynamic sixing based on channel implementation.
- */
-#define MCTP_MTU	64
+/* Baseline maximum size of a MCTP packet */
+#define MCTP_BMTU_PAYLOAD	64
+#define MCTP_BMTU		(MCTP_BMTU_PAYLOAD + sizeof(struct mctp_hdr))
 
 /* packet buffers */
 
-/* Allow a little space before the MCTP header in the packet, for bindings that
- * may add their own header
- */
-#define MCTP_PKTBUF_BINDING_PAD	2
-
-#define MCTP_PKTBUF_SIZE	(MCTP_PKTBUF_BINDING_PAD + \
-		(sizeof(struct mctp_hdr) + MCTP_MTU))
-
 struct mctp_pktbuf {
-	unsigned char	data[MCTP_PKTBUF_SIZE];
-	uint8_t		start, end;
-	uint8_t		mctp_hdr_off;
+	size_t		start, end, size;
+	size_t		mctp_hdr_off;
 	struct mctp_pktbuf *next;
+	unsigned char	data[];
 };
 
-struct mctp_pktbuf *mctp_pktbuf_alloc(uint8_t len);
+struct mctp_binding;
+
+struct mctp_pktbuf *mctp_pktbuf_alloc(struct mctp_binding *hw, size_t len);
 void mctp_pktbuf_free(struct mctp_pktbuf *pkt);
 struct mctp_hdr *mctp_pktbuf_hdr(struct mctp_pktbuf *pkt);
 void *mctp_pktbuf_data(struct mctp_pktbuf *pkt);
 uint8_t mctp_pktbuf_size(struct mctp_pktbuf *pkt);
-void *mctp_pktbuf_alloc_start(struct mctp_pktbuf *pkt, uint8_t size);
-void *mctp_pktbuf_alloc_end(struct mctp_pktbuf *pkt, uint8_t size);
-int mctp_pktbuf_push(struct mctp_pktbuf *pkt, void *data, uint8_t len);
+void *mctp_pktbuf_alloc_start(struct mctp_pktbuf *pkt, size_t size);
+void *mctp_pktbuf_alloc_end(struct mctp_pktbuf *pkt, size_t size);
+int mctp_pktbuf_push(struct mctp_pktbuf *pkt, void *data, size_t len);
 
 /* MCTP core */
 struct mctp;
 struct mctp_bus;
-struct mctp_binding;
 
 struct mctp *mctp_init(void);
 
@@ -90,6 +82,8 @@
 	uint8_t		version;
 	struct mctp_bus	*bus;
 	struct mctp	*mctp;
+	int		pkt_size;
+	int		pkt_pad;
 	int		(*tx)(struct mctp_binding *binding,
 				struct mctp_pktbuf *pkt);
 };
diff --git a/serial.c b/serial.c
index 7e27b1c..081538f 100644
--- a/serial.c
+++ b/serial.c
@@ -149,7 +149,7 @@
 static void mctp_serial_start_packet(struct mctp_binding_serial *serial,
 		uint8_t len)
 {
-	serial->rx_pkt = mctp_pktbuf_alloc(len);
+	serial->rx_pkt = mctp_pktbuf_alloc(&serial->binding, len);
 }
 
 static void mctp_rx_consume_one(struct mctp_binding_serial *serial,
@@ -183,8 +183,8 @@
 		}
 		break;
 	case STATE_WAIT_LEN:
-		if (c > (MCTP_MTU + sizeof(struct mctp_hdr))
-				|| c < sizeof(struct mctp_hdr)) {
+		if (c > serial->binding.pkt_size ||
+				c < sizeof(struct mctp_hdr)) {
 			mctp_prdebug("invalid size %d", c);
 			serial->rx_state = STATE_WAIT_SYNC_START;
 		} else {
@@ -305,6 +305,8 @@
 	serial->rx_pkt = NULL;
 	serial->binding.name = "serial";
 	serial->binding.version = 1;
+	serial->binding.pkt_size = MCTP_BMTU;
+	serial->binding.pkt_pad = 0;
 
 	serial->binding.tx = mctp_binding_serial_tx;
 
diff --git a/tests/test-utils.c b/tests/test-utils.c
index 71de8a3..dc0a5f3 100644
--- a/tests/test-utils.c
+++ b/tests/test-utils.c
@@ -27,6 +27,8 @@
 	test->binding.name = "test";
 	test->binding.version = 1;
 	test->binding.tx = mctp_binding_test_tx;
+	test->binding.pkt_size = MCTP_BMTU;
+	test->binding.pkt_pad = 0;
 	return test;
 }
 
@@ -35,7 +37,7 @@
 {
 	struct mctp_pktbuf *pkt;
 
-	pkt = mctp_pktbuf_alloc(len);
+	pkt = mctp_pktbuf_alloc(&test->binding, len);
 	assert(pkt);
 	memcpy(mctp_pktbuf_hdr(pkt), buf, len);
 	mctp_bus_rx(&test->binding, pkt);