diff --git a/astlpc.c b/astlpc.c
index 0011777..d8129d1 100644
--- a/astlpc.c
+++ b/astlpc.c
@@ -56,6 +56,7 @@
 
 	uint8_t mode;
 	uint16_t version;
+	uint32_t requested_mtu;
 
 	/* direct ops data */
 	struct mctp_binding_astlpc_ops ops;
@@ -379,6 +380,13 @@
 	sz &= ~0xfUL;
 	sz = ASTLPC_PACKET_SIZE(MCTP_PACKET_SIZE(sz));
 
+	if (astlpc->requested_mtu) {
+		size_t r;
+
+		r = ASTLPC_PACKET_SIZE(MCTP_PACKET_SIZE(astlpc->requested_mtu));
+		sz = MIN(sz, r);
+	}
+
 	/* Flip the buffers as the names are defined in terms of the host */
 	astlpc->layout.tx.offset = control_size;
 	astlpc->layout.tx.size = sz;
@@ -386,8 +394,10 @@
 		astlpc->layout.tx.offset + astlpc->layout.tx.size;
 	astlpc->layout.rx.size = sz;
 
-	/* Sanity check that can be eliminated if asserts are off */
-	assert(mctp_astlpc_layout_validate(&astlpc->layout));
+	if (!mctp_astlpc_layout_validate(&astlpc->layout)) {
+		astlpc_prerr(astlpc, "Cannot support an MTU of %zu", sz);
+		return -EINVAL;
+	}
 
 	hdr = (struct mctp_lpcmap_hdr){
 		.magic = htobe32(ASTLPC_MCTP_MAGIC),
@@ -470,7 +480,10 @@
 		return -EINVAL;
 	}
 
-	sz = ASTLPC_PACKET_SIZE(MCTP_PACKET_SIZE(MCTP_BTU));
+	astlpc_prinfo(astlpc, "Desire an MTU of %" PRIu32 " bytes",
+		      astlpc->requested_mtu);
+
+	sz = ASTLPC_PACKET_SIZE(MCTP_PACKET_SIZE(astlpc->requested_mtu));
 	layout.rx.size = sz;
 
 	if (!mctp_astlpc_layout_validate(&layout)) {
@@ -484,7 +497,8 @@
 		return -EINVAL;
 	}
 
-	astlpc_prinfo(astlpc, "Requesting MTU of %" PRIu32 " bytes", MCTP_BTU);
+	astlpc_prinfo(astlpc, "Requesting MTU of %" PRIu32 " bytes",
+		      astlpc->requested_mtu);
 
 	return mctp_astlpc_layout_write(astlpc, &layout);
 }
@@ -666,6 +680,12 @@
 	high = MAX(astlpc->layout.rx.offset, astlpc->layout.tx.offset);
 	limit = high - low;
 
+	/* Determine the largest MTU the BMC _wants_ to support */
+	if (astlpc->requested_mtu) {
+		uint32_t req = astlpc->requested_mtu;
+
+		limit = MIN(limit, ASTLPC_PACKET_SIZE(MCTP_PACKET_SIZE(req)));
+	}
 
 	/* Determine the accepted MTU, applied both directions by convention */
 	return MCTP_BODY_SIZE(ASTLPC_BODY_SIZE(MIN(limit, layout->tx.size)));
@@ -950,6 +970,7 @@
 	memset(astlpc, 0, sizeof(*astlpc));
 	astlpc->mode = mode;
 	astlpc->lpc_map = NULL;
+	astlpc->requested_mtu = mtu;
 	astlpc->binding.name = "astlpc";
 	astlpc->binding.version = 1;
 	astlpc->binding.pkt_size = MCTP_PACKET_SIZE(mtu);
@@ -985,12 +1006,6 @@
 		return NULL;
 	}
 
-	if (mtu != MCTP_BTU) {
-		mctp_prwarn("Unable to negotiate the MTU, using %u instead",
-			    MCTP_BTU);
-		mtu = MCTP_BTU;
-	}
-
 	astlpc = __mctp_astlpc_init(mode, mtu);
 	if (!astlpc)
 		return NULL;
diff --git a/tests/test_astlpc.c b/tests/test_astlpc.c
index 6de249a..9ed99c2 100644
--- a/tests/test_astlpc.c
+++ b/tests/test_astlpc.c
@@ -165,7 +165,8 @@
 };
 
 static int endpoint_init(struct astlpc_endpoint *ep, mctp_eid_t eid,
-			 uint8_t mode, uint8_t (*kcs)[2], void *lpc_mem)
+			 uint8_t mode, uint32_t mtu, uint8_t (*kcs)[2],
+			 void *lpc_mem)
 {
 	/*
 	 * Configure the direction of the KCS interface so we know whether to
@@ -180,7 +181,7 @@
 	ep->mmio.kcs = kcs;
 
 	/* Initialise the binding */
-	ep->astlpc = mctp_astlpc_init(mode, MCTP_BTU, lpc_mem,
+	ep->astlpc = mctp_astlpc_init(mode, mtu, lpc_mem,
 				      &astlpc_direct_mmio_ops, &ep->mmio);
 	assert(ep->astlpc);
 
@@ -201,14 +202,14 @@
 	assert(ctx->lpc_mem);
 
 	/* BMC initialisation */
-	rc = endpoint_init(&ctx->bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC,
+	rc = endpoint_init(&ctx->bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
 			   &ctx->kcs, ctx->lpc_mem);
 	assert(!rc);
 	assert(ctx->kcs[MCTP_ASTLPC_KCS_REG_STATUS] & KCS_STATUS_BMC_READY);
 
 	/* Host initialisation */
 	rc = endpoint_init(&ctx->host, 9, MCTP_BINDING_ASTLPC_MODE_HOST,
-			   &ctx->kcs, ctx->lpc_mem);
+			   MCTP_BTU, &ctx->kcs, ctx->lpc_mem);
 	assert(!rc);
 
 	/* BMC processes host channel init request, alerts host */
@@ -440,8 +441,8 @@
 	assert(lpc_mem);
 
 	/* BMC initialisation */
-	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(!rc);
 
 	/* Now the BMC is initialised, break its version announcement */
@@ -449,8 +450,8 @@
 	hdr->bmc_ver_cur = ASTLPC_VER_BAD;
 
 	/* Host initialisation */
-	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(rc < 0);
 
 	endpoint_destroy(&bmc);
@@ -471,13 +472,13 @@
 	assert(lpc_mem);
 
 	/* BMC initialisation */
-	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(!rc);
 
 	/* Host initialisation */
-	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(!rc);
 
 	/* Now the host is initialised, break its version announcement */
@@ -509,16 +510,16 @@
 	assert(lpc_mem);
 
 	/* BMC initialisation */
-	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(!rc);
 
 	/* Verify the BMC binding was initialised */
 	assert(kcs[MCTP_ASTLPC_KCS_REG_STATUS] & KCS_STATUS_BMC_READY);
 
 	/* Host initialisation */
-	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(!rc);
 
 	/* Host sends channel init command */
@@ -637,8 +638,8 @@
 	astlpc_assert_tx_packet(&ctx.host, &unwritten[0], MCTP_BTU);
 
 	/* BMC comes back */
-	rc = endpoint_init(&ctx.bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &ctx.kcs,
-			   ctx.lpc_mem);
+	rc = endpoint_init(&ctx.bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &ctx.kcs, ctx.lpc_mem);
 	assert(!rc);
 	mctp_set_rx_all(ctx.bmc.mctp, rx_message, &ctx);
 
@@ -670,8 +671,8 @@
 	assert(lpc_mem);
 
 	/* BMC initialisation */
-	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(!rc);
 
 	/* Check for a command despite none present */
@@ -696,8 +697,8 @@
 	assert(lpc_mem);
 
 	/* BMC initialisation */
-	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(!rc);
 
 	/* 0x5a isn't legal in v1 or v2 */
@@ -842,16 +843,21 @@
 	struct mctp_lpcmap_hdr *hdr;
 	uint8_t kcs[2] = { 0 };
 	void *lpc_mem;
+	int rc;
 
 	/* Test harness initialisation */
 	lpc_mem = calloc(1, 1 * 1024 * 1024);
 	assert(lpc_mem);
 
 	/* BMC initialisation */
-	endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &kcs, lpc_mem);
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &kcs, lpc_mem);
+	assert(!rc);
 
 	/* Host initialisation */
-	endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, &kcs, lpc_mem);
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, MCTP_BTU,
+			   &kcs, lpc_mem);
+	assert(!rc);
 
 	/*
 	 * Now that the host has initialised the control area, break
@@ -883,7 +889,9 @@
 	assert(lpc_mem);
 
 	/* BMC initialisation */
-	endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &kcs, lpc_mem);
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &kcs, lpc_mem);
+	assert(!rc);
 
 	/*
 	 * Now that the BMC has initialised the control area, break something
@@ -893,8 +901,8 @@
 	hdr->layout.rx_size = 0;
 
 	/* Host initialisation: Fails due to bad layout */
-	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, &kcs,
-			   lpc_mem);
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, MCTP_BTU,
+			   &kcs, lpc_mem);
 	assert(rc < 0);
 
 	endpoint_destroy(&host);
@@ -915,10 +923,14 @@
 	assert(lpc_mem);
 
 	/* BMC initialisation */
-	endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, &kcs, lpc_mem);
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, MCTP_BTU,
+			   &kcs, lpc_mem);
+	assert(!rc);
 
 	/* Host initialisation */
-	endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, &kcs, lpc_mem);
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST, MCTP_BTU,
+			   &kcs, lpc_mem);
+	assert(!rc);
 
 	mctp_astlpc_poll(bmc.astlpc);
 
@@ -937,6 +949,126 @@
 	free(lpc_mem);
 }
 
+static void astlpc_test_buffers_bad_host_init(void)
+{
+	struct astlpc_endpoint host;
+	uint8_t kcs[2] = { 0 };
+	void *lpc_mem;
+	int rc;
+
+	/* Test harness initialisation */
+	lpc_mem = calloc(1, 1 * 1024 * 1024);
+	assert(lpc_mem);
+
+	host.mctp = mctp_init();
+	assert(host.mctp);
+	host.mmio.kcs = &kcs;
+	host.mmio.bmc = false;
+
+	/* Set the MTU to 0 to provoke a failure */
+	host.astlpc =
+		mctp_astlpc_init(MCTP_BINDING_ASTLPC_MODE_HOST, 0, lpc_mem,
+				 &astlpc_direct_mmio_ops, &host.mmio);
+
+	rc = mctp_register_bus(host.mctp, &host.astlpc->binding, 8);
+	assert(rc < 0);
+
+	mctp_astlpc_destroy(host.astlpc);
+	mctp_destroy(host.mctp);
+	free(lpc_mem);
+}
+
+static void astlpc_test_negotiate_increased_mtu(void)
+{
+	struct astlpc_endpoint bmc, host;
+	uint8_t kcs[2] = { 0 };
+	void *lpc_mem;
+	int rc;
+
+	/* Test harness initialisation */
+	lpc_mem = calloc(1, 1 * 1024 * 1024);
+	assert(lpc_mem);
+
+	/* BMC initialisation */
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, 3 * MCTP_BTU,
+			   &kcs, lpc_mem);
+	assert(!rc);
+
+	/* Host initialisation */
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST,
+			   2 * MCTP_BTU, &kcs, lpc_mem);
+	assert(!rc);
+
+	rc = mctp_astlpc_poll(bmc.astlpc);
+	assert(rc == 0);
+
+	rc = mctp_astlpc_poll(host.astlpc);
+	assert(rc == 0);
+
+	endpoint_destroy(&host);
+	endpoint_destroy(&bmc);
+	free(lpc_mem);
+}
+
+static void astlpc_test_negotiate_mtu_low_high(void)
+{
+	struct astlpc_endpoint bmc, host;
+	uint8_t kcs[2] = { 0 };
+	void *lpc_mem;
+	int rc;
+
+	/* Test harness initialisation */
+	lpc_mem = calloc(1, 1 * 1024 * 1024);
+	assert(lpc_mem);
+
+	/* BMC initialisation */
+	rc = endpoint_init(&bmc, 8, MCTP_BINDING_ASTLPC_MODE_BMC, 3 * MCTP_BTU,
+			   &kcs, lpc_mem);
+	assert(!rc);
+
+	/* Host initialisation with low MTU */
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST,
+			   2 * MCTP_BTU, &kcs, lpc_mem);
+	assert(!rc);
+
+	/* Process low MTU proposal */
+	rc = mctp_astlpc_poll(bmc.astlpc);
+	assert(rc == 0);
+
+	/* Accept low MTU proposal */
+	rc = mctp_astlpc_poll(host.astlpc);
+	assert(rc == 0);
+
+	assert(host.astlpc->layout.rx.size ==
+	       ASTLPC_PACKET_SIZE(MCTP_PACKET_SIZE(2 * MCTP_BTU)));
+
+	/* Tear-down the host so we can bring up a new one */
+	endpoint_destroy(&host);
+
+	/*
+	 * Bring up a new host endpoint with a higher MTU than we previously
+	 * negotiated
+	 */
+	rc = endpoint_init(&host, 9, MCTP_BINDING_ASTLPC_MODE_HOST,
+			   3 * MCTP_BTU, &kcs, lpc_mem);
+	assert(!rc);
+
+	/* Process high MTU proposal */
+	rc = mctp_astlpc_poll(bmc.astlpc);
+	assert(rc == 0);
+
+	/* Accept high MTU proposal */
+	rc = mctp_astlpc_poll(host.astlpc);
+	assert(rc == 0);
+
+	assert(host.astlpc->layout.rx.size ==
+	       ASTLPC_PACKET_SIZE(MCTP_PACKET_SIZE(3 * MCTP_BTU)));
+
+	endpoint_destroy(&host);
+	endpoint_destroy(&bmc);
+	free(lpc_mem);
+}
+
 /* clang-format off */
 #define TEST_CASE(test) { #test, test }
 static const struct {
@@ -973,6 +1105,9 @@
 	TEST_CASE(astlpc_test_buffers_bad_bmc_negotiation),
 	TEST_CASE(astlpc_test_buffers_overlap_exact),
 	TEST_CASE(astlpc_test_buffers_overlap_control),
+	TEST_CASE(astlpc_test_buffers_bad_host_init),
+	TEST_CASE(astlpc_test_negotiate_increased_mtu),
+	TEST_CASE(astlpc_test_negotiate_mtu_low_high),
 };
 /* clang-format on */