diff --git a/channeldb/channel_test.go b/channeldb/channel_test.go
index 5d203889..43747372 100644
--- a/channeldb/channel_test.go
+++ b/channeldb/channel_test.go
@@ -607,7 +607,8 @@ func TestChannelStateTransition(t *testing.T) {
 		{
 			LogIndex: 2,
 			UpdateMsg: &lnwire.UpdateAddHTLC{
-				ChanID: lnwire.ChannelID{1, 2, 3},
+				ChanID:    lnwire.ChannelID{1, 2, 3},
+				ExtraData: make([]byte, 0),
 			},
 		},
 	}
@@ -628,7 +629,9 @@ func TestChannelStateTransition(t *testing.T) {
 	if !reflect.DeepEqual(
 		dbUnsignedAckedUpdates[0], unsignedAckedUpdates[0],
 	) {
-		t.Fatalf("unexpected update")
+		t.Fatalf("unexpected update: expected %v, got %v",
+			spew.Sdump(unsignedAckedUpdates[0]),
+			spew.Sdump(dbUnsignedAckedUpdates))
 	}
 
 	// The balances, new update, the HTLCs and the changes to the fake
@@ -670,22 +673,25 @@ func TestChannelStateTransition(t *testing.T) {
 				wireSig,
 				wireSig,
 			},
+			ExtraData: make([]byte, 0),
 		},
 		LogUpdates: []LogUpdate{
 			{
 				LogIndex: 1,
 				UpdateMsg: &lnwire.UpdateAddHTLC{
-					ID:     1,
-					Amount: lnwire.NewMSatFromSatoshis(100),
-					Expiry: 25,
+					ID:        1,
+					Amount:    lnwire.NewMSatFromSatoshis(100),
+					Expiry:    25,
+					ExtraData: make([]byte, 0),
 				},
 			},
 			{
 				LogIndex: 2,
 				UpdateMsg: &lnwire.UpdateAddHTLC{
-					ID:     2,
-					Amount: lnwire.NewMSatFromSatoshis(200),
-					Expiry: 50,
+					ID:        2,
+					Amount:    lnwire.NewMSatFromSatoshis(200),
+					Expiry:    50,
+					ExtraData: make([]byte, 0),
 				},
 			},
 		},
diff --git a/channeldb/waitingproof_test.go b/channeldb/waitingproof_test.go
index ed1bf050..cb5b900f 100644
--- a/channeldb/waitingproof_test.go
+++ b/channeldb/waitingproof_test.go
@@ -5,6 +5,7 @@ import (
 
 	"reflect"
 
+	"github.com/davecgh/go-spew/spew"
 	"github.com/go-errors/errors"
 	"github.com/lightningnetwork/lnd/lnwire"
 )
@@ -23,6 +24,7 @@ func TestWaitingProofStore(t *testing.T) {
 	proof1 := NewWaitingProof(true, &lnwire.AnnounceSignatures{
 		NodeSignature:    wireSig,
 		BitcoinSignature: wireSig,
+		ExtraOpaqueData:  make([]byte, 0),
 	})
 
 	store, err := NewWaitingProofStore(db)
@@ -40,7 +42,8 @@ func TestWaitingProofStore(t *testing.T) {
 		t.Fatalf("unable retrieve proof from storage: %v", err)
 	}
 	if !reflect.DeepEqual(proof1, proof2) {
-		t.Fatal("wrong proof retrieved")
+		t.Fatalf("wrong proof retrieved: expected %v, got %v",
+			spew.Sdump(proof1), spew.Sdump(proof2))
 	}
 
 	if _, err := store.Get(proof1.OppositeKey()); err != ErrWaitingProofNotFound {
diff --git a/discovery/message_store_test.go b/discovery/message_store_test.go
index 7d0fa1c2..12286e39 100644
--- a/discovery/message_store_test.go
+++ b/discovery/message_store_test.go
@@ -64,13 +64,15 @@ func randCompressedPubKey(t *testing.T) [33]byte {
 
 func randAnnounceSignatures() *lnwire.AnnounceSignatures {
 	return &lnwire.AnnounceSignatures{
-		ShortChannelID: lnwire.NewShortChanIDFromInt(rand.Uint64()),
+		ShortChannelID:  lnwire.NewShortChanIDFromInt(rand.Uint64()),
+		ExtraOpaqueData: make([]byte, 0),
 	}
 }
 
 func randChannelUpdate() *lnwire.ChannelUpdate {
 	return &lnwire.ChannelUpdate{
-		ShortChannelID: lnwire.NewShortChanIDFromInt(rand.Uint64()),
+		ShortChannelID:  lnwire.NewShortChanIDFromInt(rand.Uint64()),
+		ExtraOpaqueData: make([]byte, 0),
 	}
 }
 
diff --git a/htlcswitch/payment_result_test.go b/htlcswitch/payment_result_test.go
index 04ff57d8..aa7cbc17 100644
--- a/htlcswitch/payment_result_test.go
+++ b/htlcswitch/payment_result_test.go
@@ -39,18 +39,21 @@ func TestNetworkResultSerialization(t *testing.T) {
 		ChanID:          chanID,
 		ID:              2,
 		PaymentPreimage: preimage,
+		ExtraData:       make([]byte, 0),
 	}
 
 	fail := &lnwire.UpdateFailHTLC{
-		ChanID: chanID,
-		ID:     1,
-		Reason: []byte{},
+		ChanID:    chanID,
+		ID:        1,
+		Reason:    []byte{},
+		ExtraData: make([]byte, 0),
 	}
 
 	fail2 := &lnwire.UpdateFailHTLC{
-		ChanID: chanID,
-		ID:     1,
-		Reason: reason[:],
+		ChanID:    chanID,
+		ID:        1,
+		Reason:    reason[:],
+		ExtraData: make([]byte, 0),
 	}
 
 	testCases := []*networkResult{
diff --git a/lnwallet/channel_test.go b/lnwallet/channel_test.go
index ead91598..27ea6ac9 100644
--- a/lnwallet/channel_test.go
+++ b/lnwallet/channel_test.go
@@ -3176,6 +3176,7 @@ func TestChanSyncOweCommitment(t *testing.T) {
 			Amount:      htlcAmt,
 			Expiry:      uint32(10),
 			OnionBlob:   fakeOnionBlob,
+			ExtraData:   make([]byte, 0),
 		}
 
 		htlcIndex, err := bobChannel.AddHTLC(h, nil)
@@ -3220,6 +3221,7 @@ func TestChanSyncOweCommitment(t *testing.T) {
 		Amount:      htlcAmt,
 		Expiry:      uint32(10),
 		OnionBlob:   fakeOnionBlob,
+		ExtraData:   make([]byte, 0),
 	}
 	aliceHtlcIndex, err := aliceChannel.AddHTLC(aliceHtlc, nil)
 	if err != nil {
diff --git a/lnwire/announcement_signatures.go b/lnwire/announcement_signatures.go
index 639704de..14341392 100644
--- a/lnwire/announcement_signatures.go
+++ b/lnwire/announcement_signatures.go
@@ -2,7 +2,6 @@ package lnwire
 
 import (
 	"io"
-	"io/ioutil"
 )
 
 // AnnounceSignatures is a direct message between two endpoints of a
@@ -40,7 +39,7 @@ type AnnounceSignatures struct {
 	// properly validate the set of signatures that cover these new fields,
 	// and ensure we're able to make upgrades to the network in a forwards
 	// compatible manner.
-	ExtraOpaqueData []byte
+	ExtraOpaqueData ExtraOpaqueData
 }
 
 // A compile time check to ensure AnnounceSignatures implements the
@@ -52,29 +51,13 @@ var _ Message = (*AnnounceSignatures)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (a *AnnounceSignatures) Decode(r io.Reader, pver uint32) error {
-	err := ReadElements(r,
+	return ReadElements(r,
 		&a.ChannelID,
 		&a.ShortChannelID,
 		&a.NodeSignature,
 		&a.BitcoinSignature,
+		&a.ExtraOpaqueData,
 	)
-	if err != nil {
-		return err
-	}
-
-	// Now that we've read out all the fields that we explicitly know of,
-	// we'll collect the remainder into the ExtraOpaqueData field. If there
-	// aren't any bytes, then we'll snip off the slice to avoid carrying
-	// around excess capacity.
-	a.ExtraOpaqueData, err = ioutil.ReadAll(r)
-	if err != nil {
-		return err
-	}
-	if len(a.ExtraOpaqueData) == 0 {
-		a.ExtraOpaqueData = nil
-	}
-
-	return nil
 }
 
 // Encode serializes the target AnnounceSignatures into the passed io.Writer
@@ -104,5 +87,5 @@ func (a *AnnounceSignatures) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (a *AnnounceSignatures) MaxPayloadLength(pver uint32) uint32 {
-	return 65533
+	return MaxMsgBody
 }
diff --git a/lnwire/channel_announcement.go b/lnwire/channel_announcement.go
index 46efeed8..de4b72b3 100644
--- a/lnwire/channel_announcement.go
+++ b/lnwire/channel_announcement.go
@@ -3,7 +3,6 @@ package lnwire
 import (
 	"bytes"
 	"io"
-	"io/ioutil"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 )
@@ -56,7 +55,7 @@ type ChannelAnnouncement struct {
 	// properly validate the set of signatures that cover these new fields,
 	// and ensure we're able to make upgrades to the network in a forwards
 	// compatible manner.
-	ExtraOpaqueData []byte
+	ExtraOpaqueData ExtraOpaqueData
 }
 
 // A compile time check to ensure ChannelAnnouncement implements the
@@ -68,7 +67,7 @@ var _ Message = (*ChannelAnnouncement)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (a *ChannelAnnouncement) Decode(r io.Reader, pver uint32) error {
-	err := ReadElements(r,
+	return ReadElements(r,
 		&a.NodeSig1,
 		&a.NodeSig2,
 		&a.BitcoinSig1,
@@ -80,24 +79,8 @@ func (a *ChannelAnnouncement) Decode(r io.Reader, pver uint32) error {
 		&a.NodeID2,
 		&a.BitcoinKey1,
 		&a.BitcoinKey2,
+		&a.ExtraOpaqueData,
 	)
-	if err != nil {
-		return err
-	}
-
-	// Now that we've read out all the fields that we explicitly know of,
-	// we'll collect the remainder into the ExtraOpaqueData field. If there
-	// aren't any bytes, then we'll snip off the slice to avoid carrying
-	// around excess capacity.
-	a.ExtraOpaqueData, err = ioutil.ReadAll(r)
-	if err != nil {
-		return err
-	}
-	if len(a.ExtraOpaqueData) == 0 {
-		a.ExtraOpaqueData = nil
-	}
-
-	return nil
 }
 
 // Encode serializes the target ChannelAnnouncement into the passed io.Writer
@@ -134,7 +117,7 @@ func (a *ChannelAnnouncement) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (a *ChannelAnnouncement) MaxPayloadLength(pver uint32) uint32 {
-	return 65533
+	return MaxMsgBody
 }
 
 // DataToSign is used to retrieve part of the announcement message which should
diff --git a/lnwire/channel_reestablish.go b/lnwire/channel_reestablish.go
index 6fa8f8ac..bfe7c53a 100644
--- a/lnwire/channel_reestablish.go
+++ b/lnwire/channel_reestablish.go
@@ -60,6 +60,11 @@ type ChannelReestablish struct {
 	// LocalUnrevokedCommitPoint is the commitment point used in the
 	// current un-revoked commitment transaction of the sending party.
 	LocalUnrevokedCommitPoint *btcec.PublicKey
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // A compile time check to ensure ChannelReestablish implements the
@@ -83,12 +88,20 @@ func (a *ChannelReestablish) Encode(w io.Writer, pver uint32) error {
 	// If the commit point wasn't sent, then we won't write out any of the
 	// remaining fields as they're optional.
 	if a.LocalUnrevokedCommitPoint == nil {
-		return nil
+		// However, we'll still write out the extra data if it's
+		// present.
+		//
+		// NOTE: This is here primarily for the quickcheck tests, in
+		// practice, we'll always populate this field.
+		return WriteElements(w, a.ExtraData)
 	}
 
 	// Otherwise, we'll write out the remaining elements.
-	return WriteElements(w, a.LastRemoteCommitSecret[:],
-		a.LocalUnrevokedCommitPoint)
+	return WriteElements(w,
+		a.LastRemoteCommitSecret[:],
+		a.LocalUnrevokedCommitPoint,
+		a.ExtraData,
+	)
 }
 
 // Decode deserializes a serialized ChannelReestablish stored in the passed
@@ -118,6 +131,9 @@ func (a *ChannelReestablish) Decode(r io.Reader, pver uint32) error {
 	var buf [32]byte
 	_, err = io.ReadFull(r, buf[:32])
 	if err == io.EOF {
+		// If there aren't any more bytes, then we'll emplace an empty
+		// extra data to make our quickcheck tests happy.
+		a.ExtraData = make([]byte, 0)
 		return nil
 	} else if err != nil {
 		return err
@@ -129,7 +145,11 @@ func (a *ChannelReestablish) Decode(r io.Reader, pver uint32) error {
 	// We'll conclude by parsing out the commitment point. We don't check
 	// the error in this case, as it has included the commit secret, then
 	// they MUST also include the commit point.
-	return ReadElement(r, &a.LocalUnrevokedCommitPoint)
+	if err = ReadElement(r, &a.LocalUnrevokedCommitPoint); err != nil {
+		return err
+	}
+
+	return a.ExtraData.Decode(r)
 }
 
 // MsgType returns the integer uniquely identifying this message type on the
@@ -145,22 +165,5 @@ func (a *ChannelReestablish) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (a *ChannelReestablish) MaxPayloadLength(pver uint32) uint32 {
-	var length uint32
-
-	// ChanID - 32 bytes
-	length += 32
-
-	// NextLocalCommitHeight - 8 bytes
-	length += 8
-
-	// RemoteCommitTailHeight - 8 bytes
-	length += 8
-
-	// LastRemoteCommitSecret - 32 bytes
-	length += 32
-
-	// LocalUnrevokedCommitPoint - 33 bytes
-	length += 33
-
-	return length
+	return MaxMsgBody
 }
diff --git a/lnwire/channel_update.go b/lnwire/channel_update.go
index 037f3d55..80000056 100644
--- a/lnwire/channel_update.go
+++ b/lnwire/channel_update.go
@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"io/ioutil"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 )
@@ -115,13 +114,10 @@ type ChannelUpdate struct {
 	// HtlcMaximumMsat is the maximum HTLC value which will be accepted.
 	HtlcMaximumMsat MilliSatoshi
 
-	// ExtraOpaqueData is the set of data that was appended to this
-	// message, some of which we may not actually know how to iterate or
-	// parse. By holding onto this data, we ensure that we're able to
-	// properly validate the set of signatures that cover these new fields,
-	// and ensure we're able to make upgrades to the network in a forwards
-	// compatible manner.
-	ExtraOpaqueData []byte
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraOpaqueData ExtraOpaqueData
 }
 
 // A compile time check to ensure ChannelUpdate implements the lnwire.Message
@@ -156,19 +152,7 @@ func (a *ChannelUpdate) Decode(r io.Reader, pver uint32) error {
 		}
 	}
 
-	// Now that we've read out all the fields that we explicitly know of,
-	// we'll collect the remainder into the ExtraOpaqueData field. If there
-	// aren't any bytes, then we'll snip off the slice to avoid carrying
-	// around excess capacity.
-	a.ExtraOpaqueData, err = ioutil.ReadAll(r)
-	if err != nil {
-		return err
-	}
-	if len(a.ExtraOpaqueData) == 0 {
-		a.ExtraOpaqueData = nil
-	}
-
-	return nil
+	return a.ExtraOpaqueData.Decode(r)
 }
 
 // Encode serializes the target ChannelUpdate into the passed io.Writer
@@ -201,7 +185,7 @@ func (a *ChannelUpdate) Encode(w io.Writer, pver uint32) error {
 	}
 
 	// Finally, append any extra opaque data.
-	return WriteElements(w, a.ExtraOpaqueData)
+	return a.ExtraOpaqueData.Encode(w)
 }
 
 // MsgType returns the integer uniquely identifying this message type on the
@@ -217,7 +201,7 @@ func (a *ChannelUpdate) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (a *ChannelUpdate) MaxPayloadLength(pver uint32) uint32 {
-	return 65533
+	return MaxMsgBody
 }
 
 // DataToSign is used to retrieve part of the announcement message which should
@@ -250,7 +234,7 @@ func (a *ChannelUpdate) DataToSign() ([]byte, error) {
 	}
 
 	// Finally, append any extra opaque data.
-	if err := WriteElements(&w, a.ExtraOpaqueData); err != nil {
+	if err := a.ExtraOpaqueData.Encode(&w); err != nil {
 		return nil, err
 	}
 
diff --git a/lnwire/closing_signed.go b/lnwire/closing_signed.go
index 91b90646..7732715b 100644
--- a/lnwire/closing_signed.go
+++ b/lnwire/closing_signed.go
@@ -27,6 +27,11 @@ type ClosingSigned struct {
 
 	// Signature is for the proposed channel close transaction.
 	Signature Sig
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewClosingSigned creates a new empty ClosingSigned message.
@@ -49,7 +54,9 @@ var _ Message = (*ClosingSigned)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (c *ClosingSigned) Decode(r io.Reader, pver uint32) error {
-	return ReadElements(r, &c.ChannelID, &c.FeeSatoshis, &c.Signature)
+	return ReadElements(
+		r, &c.ChannelID, &c.FeeSatoshis, &c.Signature, &c.ExtraData,
+	)
 }
 
 // Encode serializes the target ClosingSigned into the passed io.Writer
@@ -57,7 +64,9 @@ func (c *ClosingSigned) Decode(r io.Reader, pver uint32) error {
 //
 // This is part of the lnwire.Message interface.
 func (c *ClosingSigned) Encode(w io.Writer, pver uint32) error {
-	return WriteElements(w, c.ChannelID, c.FeeSatoshis, c.Signature)
+	return WriteElements(
+		w, c.ChannelID, c.FeeSatoshis, c.Signature, c.ExtraData,
+	)
 }
 
 // MsgType returns the integer uniquely identifying this message type on the
@@ -73,16 +82,5 @@ func (c *ClosingSigned) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *ClosingSigned) MaxPayloadLength(uint32) uint32 {
-	var length uint32
-
-	// ChannelID - 32 bytes
-	length += 32
-
-	// FeeSatoshis - 8 bytes
-	length += 8
-
-	// Signature - 64 bytes
-	length += 64
-
-	return length
+	return MaxMsgBody
 }
diff --git a/lnwire/commit_sig.go b/lnwire/commit_sig.go
index f15a9738..8856389f 100644
--- a/lnwire/commit_sig.go
+++ b/lnwire/commit_sig.go
@@ -34,11 +34,18 @@ type CommitSig struct {
 	// should be signed, for each incoming HTLC the HTLC timeout
 	// transaction should be signed.
 	HtlcSigs []Sig
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewCommitSig creates a new empty CommitSig message.
 func NewCommitSig() *CommitSig {
-	return &CommitSig{}
+	return &CommitSig{
+		ExtraData: make([]byte, 0),
+	}
 }
 
 // A compile time check to ensure CommitSig implements the lnwire.Message
@@ -54,6 +61,7 @@ func (c *CommitSig) Decode(r io.Reader, pver uint32) error {
 		&c.ChanID,
 		&c.CommitSig,
 		&c.HtlcSigs,
+		&c.ExtraData,
 	)
 }
 
@@ -66,6 +74,7 @@ func (c *CommitSig) Encode(w io.Writer, pver uint32) error {
 		c.ChanID,
 		c.CommitSig,
 		c.HtlcSigs,
+		c.ExtraData,
 	)
 }
 
@@ -82,8 +91,7 @@ func (c *CommitSig) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *CommitSig) MaxPayloadLength(uint32) uint32 {
-	// 32 + 64 + 2 + max_allowed_htlcs
-	return MaxMessagePayload
+	return MaxMsgBody
 }
 
 // TargetChanID returns the channel id of the link for which this message is
diff --git a/lnwire/error.go b/lnwire/error.go
index 19911d1f..02c07aea 100644
--- a/lnwire/error.go
+++ b/lnwire/error.go
@@ -123,8 +123,7 @@ func (c *Error) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *Error) MaxPayloadLength(uint32) uint32 {
-	// 32 + 2 + 65501
-	return MaxMessagePayload
+	return MaxMsgBody
 }
 
 // isASCII is a helper method that checks whether all bytes in `data` would be
diff --git a/lnwire/funding_created.go b/lnwire/funding_created.go
index c14321ec..437b1b6a 100644
--- a/lnwire/funding_created.go
+++ b/lnwire/funding_created.go
@@ -24,6 +24,11 @@ type FundingCreated struct {
 	// CommitSig is Alice's signature from Bob's version of the commitment
 	// transaction.
 	CommitSig Sig
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // A compile time check to ensure FundingCreated implements the lnwire.Message
@@ -36,7 +41,10 @@ var _ Message = (*FundingCreated)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (f *FundingCreated) Encode(w io.Writer, pver uint32) error {
-	return WriteElements(w, f.PendingChannelID[:], f.FundingPoint, f.CommitSig)
+	return WriteElements(
+		w, f.PendingChannelID[:], f.FundingPoint, f.CommitSig,
+		f.ExtraData,
+	)
 }
 
 // Decode deserializes the serialized FundingCreated stored in the passed
@@ -45,7 +53,10 @@ func (f *FundingCreated) Encode(w io.Writer, pver uint32) error {
 //
 // This is part of the lnwire.Message interface.
 func (f *FundingCreated) Decode(r io.Reader, pver uint32) error {
-	return ReadElements(r, f.PendingChannelID[:], &f.FundingPoint, &f.CommitSig)
+	return ReadElements(
+		r, f.PendingChannelID[:], &f.FundingPoint, &f.CommitSig,
+		&f.ExtraData,
+	)
 }
 
 // MsgType returns the uint32 code which uniquely identifies this message as a
@@ -61,6 +72,5 @@ func (f *FundingCreated) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (f *FundingCreated) MaxPayloadLength(uint32) uint32 {
-	// 32 + 32 + 2 + 64
-	return 130
+	return MaxMsgBody
 }
diff --git a/lnwire/funding_locked.go b/lnwire/funding_locked.go
index c441b0be..1eeddfb6 100644
--- a/lnwire/funding_locked.go
+++ b/lnwire/funding_locked.go
@@ -19,6 +19,11 @@ type FundingLocked struct {
 	// NextPerCommitmentPoint is the secret that can be used to revoke the
 	// next commitment transaction for the channel.
 	NextPerCommitmentPoint *btcec.PublicKey
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewFundingLocked creates a new FundingLocked message, populating it with the
@@ -27,6 +32,7 @@ func NewFundingLocked(cid ChannelID, npcp *btcec.PublicKey) *FundingLocked {
 	return &FundingLocked{
 		ChanID:                 cid,
 		NextPerCommitmentPoint: npcp,
+		ExtraData:              make([]byte, 0),
 	}
 }
 
@@ -42,7 +48,9 @@ var _ Message = (*FundingLocked)(nil)
 func (c *FundingLocked) Decode(r io.Reader, pver uint32) error {
 	return ReadElements(r,
 		&c.ChanID,
-		&c.NextPerCommitmentPoint)
+		&c.NextPerCommitmentPoint,
+		&c.ExtraData,
+	)
 }
 
 // Encode serializes the target FundingLocked message into the passed io.Writer
@@ -53,7 +61,9 @@ func (c *FundingLocked) Decode(r io.Reader, pver uint32) error {
 func (c *FundingLocked) Encode(w io.Writer, pver uint32) error {
 	return WriteElements(w,
 		c.ChanID,
-		c.NextPerCommitmentPoint)
+		c.NextPerCommitmentPoint,
+		c.ExtraData,
+	)
 }
 
 // MsgType returns the uint32 code which uniquely identifies this message as a
@@ -70,14 +80,5 @@ func (c *FundingLocked) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *FundingLocked) MaxPayloadLength(uint32) uint32 {
-	var length uint32
-
-	// ChanID - 32 bytes
-	length += 32
-
-	// NextPerCommitmentPoint - 33 bytes
-	length += 33
-
-	// 65 bytes
-	return length
+	return MaxMsgBody
 }
diff --git a/lnwire/funding_signed.go b/lnwire/funding_signed.go
index 620f8b37..1ef15568 100644
--- a/lnwire/funding_signed.go
+++ b/lnwire/funding_signed.go
@@ -13,6 +13,11 @@ type FundingSigned struct {
 	// CommitSig is Bob's signature for Alice's version of the commitment
 	// transaction.
 	CommitSig Sig
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // A compile time check to ensure FundingSigned implements the lnwire.Message
@@ -25,7 +30,7 @@ var _ Message = (*FundingSigned)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (f *FundingSigned) Encode(w io.Writer, pver uint32) error {
-	return WriteElements(w, f.ChanID, f.CommitSig)
+	return WriteElements(w, f.ChanID, f.CommitSig, f.ExtraData)
 }
 
 // Decode deserializes the serialized FundingSigned stored in the passed
@@ -34,7 +39,7 @@ func (f *FundingSigned) Encode(w io.Writer, pver uint32) error {
 //
 // This is part of the lnwire.Message interface.
 func (f *FundingSigned) Decode(r io.Reader, pver uint32) error {
-	return ReadElements(r, &f.ChanID, &f.CommitSig)
+	return ReadElements(r, &f.ChanID, &f.CommitSig, &f.ExtraData)
 }
 
 // MsgType returns the uint32 code which uniquely identifies this message as a
@@ -50,6 +55,5 @@ func (f *FundingSigned) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (f *FundingSigned) MaxPayloadLength(uint32) uint32 {
-	// 32 + 64
-	return 96
+	return MaxMsgBody
 }
diff --git a/lnwire/gossip_timestamp_range.go b/lnwire/gossip_timestamp_range.go
index 3c28cd05..fb62e272 100644
--- a/lnwire/gossip_timestamp_range.go
+++ b/lnwire/gossip_timestamp_range.go
@@ -24,6 +24,11 @@ type GossipTimestampRange struct {
 	// NOT send any announcements that have a timestamp greater than
 	// FirstTimestamp + TimestampRange.
 	TimestampRange uint32
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewGossipTimestampRange creates a new empty GossipTimestampRange message.
@@ -44,6 +49,7 @@ func (g *GossipTimestampRange) Decode(r io.Reader, pver uint32) error {
 		g.ChainHash[:],
 		&g.FirstTimestamp,
 		&g.TimestampRange,
+		&g.ExtraData,
 	)
 }
 
@@ -56,6 +62,7 @@ func (g *GossipTimestampRange) Encode(w io.Writer, pver uint32) error {
 		g.ChainHash[:],
 		g.FirstTimestamp,
 		g.TimestampRange,
+		g.ExtraData,
 	)
 }
 
@@ -73,8 +80,5 @@ func (g *GossipTimestampRange) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (g *GossipTimestampRange) MaxPayloadLength(uint32) uint32 {
-	// 32 + 4 + 4
-	//
-	// TODO(roasbeef): update to 8 byte timestmaps?
-	return 40
+	return MaxMsgBody
 }
diff --git a/lnwire/init_message.go b/lnwire/init_message.go
index e1ddbb01..4e33fbb6 100644
--- a/lnwire/init_message.go
+++ b/lnwire/init_message.go
@@ -20,6 +20,11 @@ type Init struct {
 	// message, any GlobalFeatures should be merged into the unified
 	// Features field.
 	Features *RawFeatureVector
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewInitMessage creates new instance of init message object.
@@ -27,6 +32,7 @@ func NewInitMessage(gf *RawFeatureVector, f *RawFeatureVector) *Init {
 	return &Init{
 		GlobalFeatures: gf,
 		Features:       f,
+		ExtraData:      make([]byte, 0),
 	}
 }
 
@@ -42,6 +48,7 @@ func (msg *Init) Decode(r io.Reader, pver uint32) error {
 	return ReadElements(r,
 		&msg.GlobalFeatures,
 		&msg.Features,
+		&msg.ExtraData,
 	)
 }
 
@@ -53,6 +60,7 @@ func (msg *Init) Encode(w io.Writer, pver uint32) error {
 	return WriteElements(w,
 		msg.GlobalFeatures,
 		msg.Features,
+		msg.ExtraData,
 	)
 }
 
@@ -69,5 +77,5 @@ func (msg *Init) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (msg *Init) MaxPayloadLength(uint32) uint32 {
-	return 2 + 2 + maxAllowedSize + 2 + maxAllowedSize
+	return MaxMsgBody
 }
diff --git a/lnwire/lnwire_test.go b/lnwire/lnwire_test.go
index ea90f3c0..0c8cf475 100644
--- a/lnwire/lnwire_test.go
+++ b/lnwire/lnwire_test.go
@@ -440,7 +440,9 @@ func TestLightningWireProtocol(t *testing.T) {
 			v[0] = reflect.ValueOf(req)
 		},
 		MsgFundingCreated: func(v []reflect.Value, r *rand.Rand) {
-			req := FundingCreated{}
+			req := FundingCreated{
+				ExtraData: make([]byte, 0),
+			}
 
 			if _, err := r.Read(req.PendingChannelID[:]); err != nil {
 				t.Fatalf("unable to generate pending chan id: %v", err)
@@ -471,7 +473,8 @@ func TestLightningWireProtocol(t *testing.T) {
 			}
 
 			req := FundingSigned{
-				ChanID: ChannelID(c),
+				ChanID:    ChannelID(c),
+				ExtraData: make([]byte, 0),
 			}
 			req.CommitSig, err = NewSigFromSignature(testSig)
 			if err != nil {
@@ -502,6 +505,7 @@ func TestLightningWireProtocol(t *testing.T) {
 		MsgClosingSigned: func(v []reflect.Value, r *rand.Rand) {
 			req := ClosingSigned{
 				FeeSatoshis: btcutil.Amount(r.Int63()),
+				ExtraData:   make([]byte, 0),
 			}
 			var err error
 			req.Signature, err = NewSigFromSignature(testSig)
@@ -570,8 +574,9 @@ func TestLightningWireProtocol(t *testing.T) {
 		MsgChannelAnnouncement: func(v []reflect.Value, r *rand.Rand) {
 			var err error
 			req := ChannelAnnouncement{
-				ShortChannelID: NewShortChanIDFromInt(uint64(r.Int63())),
-				Features:       randRawFeatureVector(r),
+				ShortChannelID:  NewShortChanIDFromInt(uint64(r.Int63())),
+				Features:        randRawFeatureVector(r),
+				ExtraOpaqueData: make([]byte, 0),
 			}
 			req.NodeSig1, err = NewSigFromSignature(testSig)
 			if err != nil {
@@ -643,6 +648,7 @@ func TestLightningWireProtocol(t *testing.T) {
 					G: uint8(r.Int31()),
 					B: uint8(r.Int31()),
 				},
+				ExtraOpaqueData: make([]byte, 0),
 			}
 			req.Signature, err = NewSigFromSignature(testSig)
 			if err != nil {
@@ -698,6 +704,7 @@ func TestLightningWireProtocol(t *testing.T) {
 				HtlcMaximumMsat: maxHtlc,
 				BaseFee:         uint32(r.Int31()),
 				FeeRate:         uint32(r.Int31()),
+				ExtraOpaqueData: make([]byte, 0),
 			}
 			req.Signature, err = NewSigFromSignature(testSig)
 			if err != nil {
@@ -726,7 +733,8 @@ func TestLightningWireProtocol(t *testing.T) {
 		MsgAnnounceSignatures: func(v []reflect.Value, r *rand.Rand) {
 			var err error
 			req := AnnounceSignatures{
-				ShortChannelID: NewShortChanIDFromInt(uint64(r.Int63())),
+				ShortChannelID:  NewShortChanIDFromInt(uint64(r.Int63())),
+				ExtraOpaqueData: make([]byte, 0),
 			}
 
 			req.NodeSignature, err = NewSigFromSignature(testSig)
@@ -763,6 +771,7 @@ func TestLightningWireProtocol(t *testing.T) {
 			req := ChannelReestablish{
 				NextLocalCommitHeight:  uint64(r.Int63()),
 				RemoteCommitTailHeight: uint64(r.Int63()),
+				ExtraData:              make([]byte, 0),
 			}
 
 			// With a 50/50 probability, we'll include the
@@ -785,7 +794,9 @@ func TestLightningWireProtocol(t *testing.T) {
 			v[0] = reflect.ValueOf(req)
 		},
 		MsgQueryShortChanIDs: func(v []reflect.Value, r *rand.Rand) {
-			req := QueryShortChanIDs{}
+			req := QueryShortChanIDs{
+				ExtraData: make([]byte, 0),
+			}
 
 			// With a 50/50 change, we'll either use zlib encoding,
 			// or regular encoding.
@@ -812,6 +823,7 @@ func TestLightningWireProtocol(t *testing.T) {
 			req := ReplyChannelRange{
 				FirstBlockHeight: uint32(r.Int31()),
 				NumBlocks:        uint32(r.Int31()),
+				ExtraData:        make([]byte, 0),
 			}
 
 			if _, err := rand.Read(req.ChainHash[:]); err != nil {
diff --git a/lnwire/node_announcement.go b/lnwire/node_announcement.go
index 35534352..62414d4b 100644
--- a/lnwire/node_announcement.go
+++ b/lnwire/node_announcement.go
@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"image/color"
 	"io"
-	"io/ioutil"
 	"net"
 	"unicode/utf8"
 )
@@ -98,7 +97,7 @@ type NodeAnnouncement struct {
 	// properly validate the set of signatures that cover these new fields,
 	// and ensure we're able to make upgrades to the network in a forwards
 	// compatible manner.
-	ExtraOpaqueData []byte
+	ExtraOpaqueData ExtraOpaqueData
 }
 
 // A compile time check to ensure NodeAnnouncement implements the
@@ -110,7 +109,7 @@ var _ Message = (*NodeAnnouncement)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (a *NodeAnnouncement) Decode(r io.Reader, pver uint32) error {
-	err := ReadElements(r,
+	return ReadElements(r,
 		&a.Signature,
 		&a.Features,
 		&a.Timestamp,
@@ -118,24 +117,8 @@ func (a *NodeAnnouncement) Decode(r io.Reader, pver uint32) error {
 		&a.RGBColor,
 		&a.Alias,
 		&a.Addresses,
+		&a.ExtraOpaqueData,
 	)
-	if err != nil {
-		return err
-	}
-
-	// Now that we've read out all the fields that we explicitly know of,
-	// we'll collect the remainder into the ExtraOpaqueData field. If there
-	// aren't any bytes, then we'll snip off the slice to avoid carrying
-	// around excess capacity.
-	a.ExtraOpaqueData, err = ioutil.ReadAll(r)
-	if err != nil {
-		return err
-	}
-	if len(a.ExtraOpaqueData) == 0 {
-		a.ExtraOpaqueData = nil
-	}
-
-	return nil
 }
 
 // Encode serializes the target NodeAnnouncement into the passed io.Writer
@@ -167,7 +150,7 @@ func (a *NodeAnnouncement) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (a *NodeAnnouncement) MaxPayloadLength(pver uint32) uint32 {
-	return 65533
+	return MaxMsgBody
 }
 
 // DataToSign returns the part of the message that should be signed.
diff --git a/lnwire/onion_error_test.go b/lnwire/onion_error_test.go
index 3ec147d1..8c4c131c 100644
--- a/lnwire/onion_error_test.go
+++ b/lnwire/onion_error_test.go
@@ -20,11 +20,12 @@ var (
 	testOffset        = uint16(24)
 	sig, _            = NewSigFromSignature(testSig)
 	testChannelUpdate = ChannelUpdate{
-		Signature:      sig,
-		ShortChannelID: NewShortChanIDFromInt(1),
-		Timestamp:      1,
-		MessageFlags:   0,
-		ChannelFlags:   1,
+		Signature:       sig,
+		ShortChannelID:  NewShortChanIDFromInt(1),
+		Timestamp:       1,
+		MessageFlags:    0,
+		ChannelFlags:    1,
+		ExtraOpaqueData: make([]byte, 0),
 	}
 )
 
diff --git a/lnwire/query_channel_range.go b/lnwire/query_channel_range.go
index 9546fcd3..3bdb30e5 100644
--- a/lnwire/query_channel_range.go
+++ b/lnwire/query_channel_range.go
@@ -25,6 +25,11 @@ type QueryChannelRange struct {
 	// NumBlocks is the number of blocks beyond the first block that short
 	// channel ID's should be sent for.
 	NumBlocks uint32
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewQueryChannelRange creates a new empty QueryChannelRange message.
@@ -45,6 +50,7 @@ func (q *QueryChannelRange) Decode(r io.Reader, pver uint32) error {
 		q.ChainHash[:],
 		&q.FirstBlockHeight,
 		&q.NumBlocks,
+		&q.ExtraData,
 	)
 }
 
@@ -57,6 +63,7 @@ func (q *QueryChannelRange) Encode(w io.Writer, pver uint32) error {
 		q.ChainHash[:],
 		q.FirstBlockHeight,
 		q.NumBlocks,
+		q.ExtraData,
 	)
 }
 
@@ -73,8 +80,7 @@ func (q *QueryChannelRange) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (q *QueryChannelRange) MaxPayloadLength(uint32) uint32 {
-	// 32 + 4 + 4
-	return 40
+	return MaxMsgBody
 }
 
 // LastBlockHeight returns the last block height covered by the range of a
diff --git a/lnwire/query_short_chan_ids.go b/lnwire/query_short_chan_ids.go
index 3c2b9948..bae23d9f 100644
--- a/lnwire/query_short_chan_ids.go
+++ b/lnwire/query_short_chan_ids.go
@@ -81,6 +81,11 @@ type QueryShortChanIDs struct {
 	// ShortChanIDs is a slice of decoded short channel ID's.
 	ShortChanIDs []ShortChannelID
 
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
+
 	// noSort indicates whether or not to sort the short channel ids before
 	// writing them out.
 	//
@@ -114,8 +119,11 @@ func (q *QueryShortChanIDs) Decode(r io.Reader, pver uint32) error {
 	}
 
 	q.EncodingType, q.ShortChanIDs, err = decodeShortChanIDs(r)
+	if err != nil {
+		return err
+	}
 
-	return err
+	return q.ExtraData.Decode(r)
 }
 
 // decodeShortChanIDs decodes a set of short channel ID's that have been
@@ -292,7 +300,12 @@ func (q *QueryShortChanIDs) Encode(w io.Writer, pver uint32) error {
 
 	// Base on our encoding type, we'll write out the set of short channel
 	// ID's.
-	return encodeShortChanIDs(w, q.EncodingType, q.ShortChanIDs, q.noSort)
+	err = encodeShortChanIDs(w, q.EncodingType, q.ShortChanIDs, q.noSort)
+	if err != nil {
+		return err
+	}
+
+	return q.ExtraData.Encode(w)
 }
 
 // encodeShortChanIDs encodes the passed short channel ID's into the passed
@@ -425,5 +438,5 @@ func (q *QueryShortChanIDs) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (q *QueryShortChanIDs) MaxPayloadLength(uint32) uint32 {
-	return MaxMessagePayload
+	return MaxMsgBody
 }
diff --git a/lnwire/reply_channel_range.go b/lnwire/reply_channel_range.go
index 3ff5dd4b..5167cc5a 100644
--- a/lnwire/reply_channel_range.go
+++ b/lnwire/reply_channel_range.go
@@ -37,6 +37,11 @@ type ReplyChannelRange struct {
 	// ShortChanIDs is a slice of decoded short channel ID's.
 	ShortChanIDs []ShortChannelID
 
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
+
 	// noSort indicates whether or not to sort the short channel ids before
 	// writing them out.
 	//
@@ -73,7 +78,7 @@ func (c *ReplyChannelRange) Decode(r io.Reader, pver uint32) error {
 		return err
 	}
 
-	return err
+	return c.ExtraData.Decode(r)
 }
 
 // Encode serializes the target ReplyChannelRange into the passed io.Writer
@@ -96,7 +101,7 @@ func (c *ReplyChannelRange) Encode(w io.Writer, pver uint32) error {
 		return err
 	}
 
-	return nil
+	return c.ExtraData.Encode(w)
 }
 
 // MsgType returns the integer uniquely identifying this message type on the
@@ -112,7 +117,7 @@ func (c *ReplyChannelRange) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *ReplyChannelRange) MaxPayloadLength(uint32) uint32 {
-	return MaxMessagePayload
+	return MaxMsgBody
 }
 
 // LastBlockHeight returns the last block height covered by the range of a
diff --git a/lnwire/reply_channel_range_test.go b/lnwire/reply_channel_range_test.go
index d656db55..ff341495 100644
--- a/lnwire/reply_channel_range_test.go
+++ b/lnwire/reply_channel_range_test.go
@@ -72,6 +72,7 @@ func TestReplyChannelRangeEmpty(t *testing.T) {
 				Complete:         1,
 				EncodingType:     test.encType,
 				ShortChanIDs:     nil,
+				ExtraData:        make([]byte, 0),
 			}
 
 			// First decode the hex string in the test case into a
diff --git a/lnwire/reply_short_chan_ids_end.go b/lnwire/reply_short_chan_ids_end.go
index d77aa0b5..92f1e8fc 100644
--- a/lnwire/reply_short_chan_ids_end.go
+++ b/lnwire/reply_short_chan_ids_end.go
@@ -22,6 +22,11 @@ type ReplyShortChanIDsEnd struct {
 	// set of short chan ID's in the corresponding QueryShortChanIDs
 	// message.
 	Complete uint8
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewReplyShortChanIDsEnd creates a new empty ReplyShortChanIDsEnd message.
@@ -41,6 +46,7 @@ func (c *ReplyShortChanIDsEnd) Decode(r io.Reader, pver uint32) error {
 	return ReadElements(r,
 		c.ChainHash[:],
 		&c.Complete,
+		&c.ExtraData,
 	)
 }
 
@@ -52,6 +58,7 @@ func (c *ReplyShortChanIDsEnd) Encode(w io.Writer, pver uint32) error {
 	return WriteElements(w,
 		c.ChainHash[:],
 		c.Complete,
+		c.ExtraData,
 	)
 }
 
@@ -69,6 +76,5 @@ func (c *ReplyShortChanIDsEnd) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *ReplyShortChanIDsEnd) MaxPayloadLength(uint32) uint32 {
-	// 32 (chain hash) + 1 (complete)
-	return 33
+	return MaxMsgBody
 }
diff --git a/lnwire/revoke_and_ack.go b/lnwire/revoke_and_ack.go
index 0cfa2bc2..b187fae6 100644
--- a/lnwire/revoke_and_ack.go
+++ b/lnwire/revoke_and_ack.go
@@ -30,11 +30,18 @@ type RevokeAndAck struct {
 	// create the proper revocation key used within the commitment
 	// transaction.
 	NextRevocationKey *btcec.PublicKey
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewRevokeAndAck creates a new RevokeAndAck message.
 func NewRevokeAndAck() *RevokeAndAck {
-	return &RevokeAndAck{}
+	return &RevokeAndAck{
+		ExtraData: make([]byte, 0),
+	}
 }
 
 // A compile time check to ensure RevokeAndAck implements the lnwire.Message
@@ -50,6 +57,7 @@ func (c *RevokeAndAck) Decode(r io.Reader, pver uint32) error {
 		&c.ChanID,
 		c.Revocation[:],
 		&c.NextRevocationKey,
+		&c.ExtraData,
 	)
 }
 
@@ -62,6 +70,7 @@ func (c *RevokeAndAck) Encode(w io.Writer, pver uint32) error {
 		c.ChanID,
 		c.Revocation[:],
 		c.NextRevocationKey,
+		c.ExtraData,
 	)
 }
 
@@ -78,8 +87,7 @@ func (c *RevokeAndAck) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *RevokeAndAck) MaxPayloadLength(uint32) uint32 {
-	// 32 + 32 + 33
-	return 97
+	return MaxMsgBody
 }
 
 // TargetChanID returns the channel id of the link for which this message is
diff --git a/lnwire/shutdown.go b/lnwire/shutdown.go
index 94d10a90..e27681e4 100644
--- a/lnwire/shutdown.go
+++ b/lnwire/shutdown.go
@@ -15,6 +15,11 @@ type Shutdown struct {
 
 	// Address is the script to which the channel funds will be paid.
 	Address DeliveryAddress
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // DeliveryAddress is used to communicate the address to which funds from a
@@ -48,7 +53,7 @@ var _ Message = (*Shutdown)(nil)
 //
 // This is part of the lnwire.Message interface.
 func (s *Shutdown) Decode(r io.Reader, pver uint32) error {
-	return ReadElements(r, &s.ChannelID, &s.Address)
+	return ReadElements(r, &s.ChannelID, &s.Address, &s.ExtraData)
 }
 
 // Encode serializes the target Shutdown into the passed io.Writer observing
@@ -56,7 +61,7 @@ func (s *Shutdown) Decode(r io.Reader, pver uint32) error {
 //
 // This is part of the lnwire.Message interface.
 func (s *Shutdown) Encode(w io.Writer, pver uint32) error {
-	return WriteElements(w, s.ChannelID, s.Address)
+	return WriteElements(w, s.ChannelID, s.Address, s.ExtraData)
 }
 
 // MsgType returns the integer uniquely identifying this message type on the
@@ -72,16 +77,5 @@ func (s *Shutdown) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (s *Shutdown) MaxPayloadLength(pver uint32) uint32 {
-	var length uint32
-
-	// ChannelID - 32bytes
-	length += 32
-
-	// Len - 2 bytes
-	length += 2
-
-	// ScriptPubKey - maximum delivery address size.
-	length += deliveryAddressMaxSize
-
-	return length
+	return MaxMsgBody
 }
diff --git a/lnwire/update_add_htlc.go b/lnwire/update_add_htlc.go
index 028c6320..9211d39f 100644
--- a/lnwire/update_add_htlc.go
+++ b/lnwire/update_add_htlc.go
@@ -52,6 +52,11 @@ type UpdateAddHTLC struct {
 	// should strip off a layer of encryption, exposing the next hop to be
 	// used in the subsequent UpdateAddHTLC message.
 	OnionBlob [OnionPacketSize]byte
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewUpdateAddHTLC returns a new empty UpdateAddHTLC message.
@@ -75,6 +80,7 @@ func (c *UpdateAddHTLC) Decode(r io.Reader, pver uint32) error {
 		c.PaymentHash[:],
 		&c.Expiry,
 		c.OnionBlob[:],
+		&c.ExtraData,
 	)
 }
 
@@ -90,6 +96,7 @@ func (c *UpdateAddHTLC) Encode(w io.Writer, pver uint32) error {
 		c.PaymentHash[:],
 		c.Expiry,
 		c.OnionBlob[:],
+		c.ExtraData,
 	)
 }
 
@@ -106,8 +113,7 @@ func (c *UpdateAddHTLC) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *UpdateAddHTLC) MaxPayloadLength(uint32) uint32 {
-	// 1450
-	return 32 + 8 + 4 + 8 + 32 + 1366
+	return MaxMsgBody
 }
 
 // TargetChanID returns the channel id of the link for which this message is
diff --git a/lnwire/update_fail_htlc.go b/lnwire/update_fail_htlc.go
index 194f2ecd..09666ac2 100644
--- a/lnwire/update_fail_htlc.go
+++ b/lnwire/update_fail_htlc.go
@@ -26,6 +26,11 @@ type UpdateFailHTLC struct {
 	// failed. This blob is only fully decryptable by the initiator of the
 	// HTLC message.
 	Reason OpaqueReason
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // A compile time check to ensure UpdateFailHTLC implements the lnwire.Message
@@ -41,6 +46,7 @@ func (c *UpdateFailHTLC) Decode(r io.Reader, pver uint32) error {
 		&c.ChanID,
 		&c.ID,
 		&c.Reason,
+		&c.ExtraData,
 	)
 }
 
@@ -53,6 +59,7 @@ func (c *UpdateFailHTLC) Encode(w io.Writer, pver uint32) error {
 		c.ChanID,
 		c.ID,
 		c.Reason,
+		c.ExtraData,
 	)
 }
 
@@ -69,21 +76,7 @@ func (c *UpdateFailHTLC) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *UpdateFailHTLC) MaxPayloadLength(uint32) uint32 {
-	var length uint32
-
-	// Length of the ChanID
-	length += 32
-
-	// Length of the ID
-	length += 8
-
-	// Length of the length opaque reason
-	length += 2
-
-	// Length of the Reason
-	length += 292
-
-	return length
+	return MaxMsgBody
 }
 
 // TargetChanID returns the channel id of the link for which this message is
diff --git a/lnwire/update_fail_malformed_htlc.go b/lnwire/update_fail_malformed_htlc.go
index 39d4b870..b28ec29f 100644
--- a/lnwire/update_fail_malformed_htlc.go
+++ b/lnwire/update_fail_malformed_htlc.go
@@ -24,6 +24,11 @@ type UpdateFailMalformedHTLC struct {
 
 	// FailureCode the exact reason why onion blob haven't been parsed.
 	FailureCode FailCode
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // A compile time check to ensure UpdateFailMalformedHTLC implements the
@@ -40,6 +45,7 @@ func (c *UpdateFailMalformedHTLC) Decode(r io.Reader, pver uint32) error {
 		&c.ID,
 		c.ShaOnionBlob[:],
 		&c.FailureCode,
+		&c.ExtraData,
 	)
 }
 
@@ -53,6 +59,7 @@ func (c *UpdateFailMalformedHTLC) Encode(w io.Writer, pver uint32) error {
 		c.ID,
 		c.ShaOnionBlob[:],
 		c.FailureCode,
+		c.ExtraData,
 	)
 }
 
@@ -70,8 +77,7 @@ func (c *UpdateFailMalformedHTLC) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *UpdateFailMalformedHTLC) MaxPayloadLength(uint32) uint32 {
-	// 32 +  8 + 32 + 2
-	return 74
+	return MaxMsgBody
 }
 
 // TargetChanID returns the channel id of the link for which this message is
diff --git a/lnwire/update_fee.go b/lnwire/update_fee.go
index 2d27c377..25ab180c 100644
--- a/lnwire/update_fee.go
+++ b/lnwire/update_fee.go
@@ -16,6 +16,11 @@ type UpdateFee struct {
 	// TODO(halseth): make SatPerKWeight when fee estimation is moved to
 	// own package. Currently this will cause an import cycle.
 	FeePerKw uint32
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewUpdateFee creates a new UpdateFee message.
@@ -38,6 +43,7 @@ func (c *UpdateFee) Decode(r io.Reader, pver uint32) error {
 	return ReadElements(r,
 		&c.ChanID,
 		&c.FeePerKw,
+		&c.ExtraData,
 	)
 }
 
@@ -49,6 +55,7 @@ func (c *UpdateFee) Encode(w io.Writer, pver uint32) error {
 	return WriteElements(w,
 		c.ChanID,
 		c.FeePerKw,
+		c.ExtraData,
 	)
 }
 
@@ -65,8 +72,7 @@ func (c *UpdateFee) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *UpdateFee) MaxPayloadLength(uint32) uint32 {
-	// 32 + 4
-	return 36
+	return MaxMsgBody
 }
 
 // TargetChanID returns the channel id of the link for which this message is
diff --git a/lnwire/update_fulfill_htlc.go b/lnwire/update_fulfill_htlc.go
index 6c0e6339..36977b1e 100644
--- a/lnwire/update_fulfill_htlc.go
+++ b/lnwire/update_fulfill_htlc.go
@@ -21,6 +21,11 @@ type UpdateFulfillHTLC struct {
 	// PaymentPreimage is the R-value preimage required to fully settle an
 	// HTLC.
 	PaymentPreimage [32]byte
+
+	// ExtraData is the set of data that was appended to this message to
+	// fill out the full maximum transport message size. These fields can
+	// be used to specify optional data such as custom TLV fields.
+	ExtraData ExtraOpaqueData
 }
 
 // NewUpdateFulfillHTLC returns a new empty UpdateFulfillHTLC.
@@ -47,6 +52,7 @@ func (c *UpdateFulfillHTLC) Decode(r io.Reader, pver uint32) error {
 		&c.ChanID,
 		&c.ID,
 		c.PaymentPreimage[:],
+		&c.ExtraData,
 	)
 }
 
@@ -59,6 +65,7 @@ func (c *UpdateFulfillHTLC) Encode(w io.Writer, pver uint32) error {
 		c.ChanID,
 		c.ID,
 		c.PaymentPreimage[:],
+		c.ExtraData,
 	)
 }
 
@@ -75,8 +82,7 @@ func (c *UpdateFulfillHTLC) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (c *UpdateFulfillHTLC) MaxPayloadLength(uint32) uint32 {
-	// 32 + 8 + 32
-	return 72
+	return MaxMsgBody
 }
 
 // TargetChanID returns the channel id of the link for which this message is