diff --git a/chain/exchange/cbor_gen.go b/chain/exchange/cbor_gen.go
index e66b6d798c4..71c75869dba 100644
--- a/chain/exchange/cbor_gen.go
+++ b/chain/exchange/cbor_gen.go
@@ -306,9 +306,9 @@ func (t *Response) UnmarshalCBOR(r io.Reader) (err error) {
 	return nil
 }
 
-var lengthBufCompactedMessages = []byte{132}
+var lengthBufCompactedMessagesCBOR = []byte{132}
 
-func (t *CompactedMessages) MarshalCBOR(w io.Writer) error {
+func (t *CompactedMessagesCBOR) MarshalCBOR(w io.Writer) error {
 	if t == nil {
 		_, err := w.Write(cbg.CborNull)
 		return err
@@ -316,12 +316,12 @@ func (t *CompactedMessages) MarshalCBOR(w io.Writer) error {
 
 	cw := cbg.NewCborWriter(w)
 
-	if _, err := cw.Write(lengthBufCompactedMessages); err != nil {
+	if _, err := cw.Write(lengthBufCompactedMessagesCBOR); err != nil {
 		return err
 	}
 
 	// t.Bls ([]*types.Message) (slice)
-	if len(t.Bls) > cbg.MaxLength {
+	if len(t.Bls) > 150000 {
 		return xerrors.Errorf("Slice value in field t.Bls was too long")
 	}
 
@@ -334,7 +334,7 @@ func (t *CompactedMessages) MarshalCBOR(w io.Writer) error {
 		}
 	}
 
-	// t.BlsIncludes ([][]uint64) (slice)
+	// t.BlsIncludes ([]exchange.messageIndices) (slice)
 	if len(t.BlsIncludes) > cbg.MaxLength {
 		return xerrors.Errorf("Slice value in field t.BlsIncludes was too long")
 	}
@@ -343,24 +343,13 @@ func (t *CompactedMessages) MarshalCBOR(w io.Writer) error {
 		return err
 	}
 	for _, v := range t.BlsIncludes {
-		if len(v) > cbg.MaxLength {
-			return xerrors.Errorf("Slice value in field v was too long")
-		}
-
-		if err := cw.WriteMajorTypeHeader(cbg.MajArray, uint64(len(v))); err != nil {
+		if err := v.MarshalCBOR(cw); err != nil {
 			return err
 		}
-		for _, v := range v {
-
-			if err := cw.WriteMajorTypeHeader(cbg.MajUnsignedInt, uint64(v)); err != nil {
-				return err
-			}
-
-		}
 	}
 
 	// t.Secpk ([]*types.SignedMessage) (slice)
-	if len(t.Secpk) > cbg.MaxLength {
+	if len(t.Secpk) > 150000 {
 		return xerrors.Errorf("Slice value in field t.Secpk was too long")
 	}
 
@@ -373,7 +362,7 @@ func (t *CompactedMessages) MarshalCBOR(w io.Writer) error {
 		}
 	}
 
-	// t.SecpkIncludes ([][]uint64) (slice)
+	// t.SecpkIncludes ([]exchange.messageIndices) (slice)
 	if len(t.SecpkIncludes) > cbg.MaxLength {
 		return xerrors.Errorf("Slice value in field t.SecpkIncludes was too long")
 	}
@@ -382,26 +371,15 @@ func (t *CompactedMessages) MarshalCBOR(w io.Writer) error {
 		return err
 	}
 	for _, v := range t.SecpkIncludes {
-		if len(v) > cbg.MaxLength {
-			return xerrors.Errorf("Slice value in field v was too long")
-		}
-
-		if err := cw.WriteMajorTypeHeader(cbg.MajArray, uint64(len(v))); err != nil {
+		if err := v.MarshalCBOR(cw); err != nil {
 			return err
 		}
-		for _, v := range v {
-
-			if err := cw.WriteMajorTypeHeader(cbg.MajUnsignedInt, uint64(v)); err != nil {
-				return err
-			}
-
-		}
 	}
 	return nil
 }
 
-func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
-	*t = CompactedMessages{}
+func (t *CompactedMessagesCBOR) UnmarshalCBOR(r io.Reader) (err error) {
+	*t = CompactedMessagesCBOR{}
 
 	cr := cbg.NewCborReader(r)
 
@@ -430,7 +408,7 @@ func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
 		return err
 	}
 
-	if extra > cbg.MaxLength {
+	if extra > 150000 {
 		return fmt.Errorf("t.Bls: array too large (%d)", extra)
 	}
 
@@ -471,7 +449,7 @@ func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
 		}
 	}
 
-	// t.BlsIncludes ([][]uint64) (slice)
+	// t.BlsIncludes ([]exchange.messageIndices) (slice)
 
 	maj, extra, err = cr.ReadHeader()
 	if err != nil {
@@ -487,7 +465,7 @@ func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
 	}
 
 	if extra > 0 {
-		t.BlsIncludes = make([][]uint64, extra)
+		t.BlsIncludes = make([]messageIndices, extra)
 	}
 
 	for i := 0; i < int(extra); i++ {
@@ -499,47 +477,13 @@ func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
 			_ = extra
 			_ = err
 
-			maj, extra, err = cr.ReadHeader()
-			if err != nil {
-				return err
-			}
-
-			if extra > cbg.MaxLength {
-				return fmt.Errorf("t.BlsIncludes[i]: array too large (%d)", extra)
-			}
-
-			if maj != cbg.MajArray {
-				return fmt.Errorf("expected cbor array")
-			}
-
-			if extra > 0 {
-				t.BlsIncludes[i] = make([]uint64, extra)
-			}
-
-			for j := 0; j < int(extra); j++ {
-				{
-					var maj byte
-					var extra uint64
-					var err error
-					_ = maj
-					_ = extra
-					_ = err
-
-					{
-
-						maj, extra, err = cr.ReadHeader()
-						if err != nil {
-							return err
-						}
-						if maj != cbg.MajUnsignedInt {
-							return fmt.Errorf("wrong type for uint64 field")
-						}
-						t.BlsIncludes[i][j] = uint64(extra)
+			{
 
-					}
+				if err := t.BlsIncludes[i].UnmarshalCBOR(cr); err != nil {
+					return xerrors.Errorf("unmarshaling t.BlsIncludes[i]: %w", err)
 				}
-			}
 
+			}
 		}
 	}
 
@@ -550,7 +494,7 @@ func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
 		return err
 	}
 
-	if extra > cbg.MaxLength {
+	if extra > 150000 {
 		return fmt.Errorf("t.Secpk: array too large (%d)", extra)
 	}
 
@@ -591,7 +535,7 @@ func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
 		}
 	}
 
-	// t.SecpkIncludes ([][]uint64) (slice)
+	// t.SecpkIncludes ([]exchange.messageIndices) (slice)
 
 	maj, extra, err = cr.ReadHeader()
 	if err != nil {
@@ -607,7 +551,7 @@ func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
 	}
 
 	if extra > 0 {
-		t.SecpkIncludes = make([][]uint64, extra)
+		t.SecpkIncludes = make([]messageIndices, extra)
 	}
 
 	for i := 0; i < int(extra); i++ {
@@ -619,47 +563,13 @@ func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
 			_ = extra
 			_ = err
 
-			maj, extra, err = cr.ReadHeader()
-			if err != nil {
-				return err
-			}
-
-			if extra > cbg.MaxLength {
-				return fmt.Errorf("t.SecpkIncludes[i]: array too large (%d)", extra)
-			}
-
-			if maj != cbg.MajArray {
-				return fmt.Errorf("expected cbor array")
-			}
-
-			if extra > 0 {
-				t.SecpkIncludes[i] = make([]uint64, extra)
-			}
-
-			for j := 0; j < int(extra); j++ {
-				{
-					var maj byte
-					var extra uint64
-					var err error
-					_ = maj
-					_ = extra
-					_ = err
-
-					{
-
-						maj, extra, err = cr.ReadHeader()
-						if err != nil {
-							return err
-						}
-						if maj != cbg.MajUnsignedInt {
-							return fmt.Errorf("wrong type for uint64 field")
-						}
-						t.SecpkIncludes[i][j] = uint64(extra)
+			{
 
-					}
+				if err := t.SecpkIncludes[i].UnmarshalCBOR(cr); err != nil {
+					return xerrors.Errorf("unmarshaling t.SecpkIncludes[i]: %w", err)
 				}
-			}
 
+			}
 		}
 	}
 
diff --git a/chain/exchange/client.go b/chain/exchange/client.go
index db39628be69..fca8249cef9 100644
--- a/chain/exchange/client.go
+++ b/chain/exchange/client.go
@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"context"
 	"fmt"
+	"io"
 	"math/rand"
 	"time"
 
@@ -23,6 +24,10 @@ import (
 	"github.com/filecoin-project/lotus/lib/peermgr"
 )
 
+// Set the max exchange message size to 120MiB. Purely based on gas numbers, we can include ~8MiB of
+// messages per block, so I've set this to 120MiB to be _very_ safe.
+const maxExchangeMessageSize = (15 * 8) << 20
+
 // client implements exchange.Client, using the libp2p ChainExchange protocol
 // as the fetching mechanism.
 type client struct {
@@ -434,10 +439,11 @@ func (c *client) sendRequestToPeer(ctx context.Context, peer peer.ID, req *Reque
 		log.Warnw("CloseWrite err", "error", err)
 	}
 
-	// Read response.
+	// Read response, limiting the size of the response to maxExchangeMessageSize as we allow a
+	// lot of messages (10k+) but they'll mostly be quite small.
 	var res Response
 	err = cborutil.ReadCborRPC(
-		bufio.NewReader(incrt.New(stream, ReadResMinSpeed, ReadResDeadline)),
+		bufio.NewReader(io.LimitReader(incrt.New(stream, ReadResMinSpeed, ReadResDeadline), maxExchangeMessageSize)),
 		&res)
 	if err != nil {
 		c.peerTracker.logFailure(peer, build.Clock.Since(connectionStart), req.Length)
diff --git a/chain/exchange/protocol.go b/chain/exchange/protocol.go
index 5e12d31cc29..cd25f4a4350 100644
--- a/chain/exchange/protocol.go
+++ b/chain/exchange/protocol.go
@@ -154,6 +154,8 @@ type BSTipSet struct {
 // FIXME: The logic to decompress this structure should belong
 //
 //	to itself, not to the consumer.
+//
+// NOTE: Max messages is: BlockMessageLimit (10k) * MaxTipsetSize (15) = 150k
 type CompactedMessages struct {
 	Bls         []*types.Message
 	BlsIncludes [][]uint64
diff --git a/chain/exchange/protocol_encoding.go b/chain/exchange/protocol_encoding.go
new file mode 100644
index 00000000000..7df00a639f9
--- /dev/null
+++ b/chain/exchange/protocol_encoding.go
@@ -0,0 +1,125 @@
+package exchange
+
+import (
+	"fmt"
+	"io"
+
+	cbg "github.com/whyrusleeping/cbor-gen"
+	xerrors "golang.org/x/xerrors"
+
+	"github.com/filecoin-project/lotus/build"
+	types "github.com/filecoin-project/lotus/chain/types"
+)
+
+// Type used for encoding/decoding compacted messages. This is a ustom type as we need custom limits.
+// - Max messages is 150,000 as that's 15 times the max block size (in messages). It needs to be
+// large enough to cover a full tipset full of full blocks.
+type CompactedMessagesCBOR struct {
+	Bls         []*types.Message `cborgen:"maxlen=150000"`
+	BlsIncludes []messageIndices
+
+	Secpk         []*types.SignedMessage `cborgen:"maxlen=150000"`
+	SecpkIncludes []messageIndices
+}
+
+// Unmarshal into the "decoding" struct, then copy into the actual struct.
+func (t *CompactedMessages) UnmarshalCBOR(r io.Reader) (err error) {
+	var c CompactedMessagesCBOR
+	if err := c.UnmarshalCBOR(r); err != nil {
+		return err
+	}
+	t.Bls = c.Bls
+	t.BlsIncludes = make([][]uint64, len(c.BlsIncludes))
+	for i, v := range c.BlsIncludes {
+		t.BlsIncludes[i] = v.v
+	}
+	t.Secpk = c.Secpk
+	t.SecpkIncludes = make([][]uint64, len(c.SecpkIncludes))
+	for i, v := range c.SecpkIncludes {
+		t.SecpkIncludes[i] = v.v
+	}
+	return nil
+}
+
+// Copy into the encoding struct, then marshal.
+func (t *CompactedMessages) MarshalCBOR(w io.Writer) error {
+	if t == nil {
+		_, err := w.Write(cbg.CborNull)
+		return err
+	}
+
+	var c CompactedMessagesCBOR
+	c.Bls = t.Bls
+	c.BlsIncludes = make([]messageIndices, len(t.BlsIncludes))
+	for i, v := range t.BlsIncludes {
+		c.BlsIncludes[i].v = v
+	}
+	c.Secpk = t.Secpk
+	c.SecpkIncludes = make([]messageIndices, len(t.SecpkIncludes))
+	for i, v := range t.SecpkIncludes {
+		c.SecpkIncludes[i].v = v
+	}
+	return c.MarshalCBOR(w)
+}
+
+// this needs to be a struct or cborgen will peak into it and ignore the Unmarshal/Marshal functions
+type messageIndices struct {
+	v []uint64
+}
+
+func (t *messageIndices) UnmarshalCBOR(r io.Reader) (err error) {
+	cr := cbg.NewCborReader(r)
+
+	maj, extra, err := cr.ReadHeader()
+	if err != nil {
+		return err
+	}
+
+	if maj != cbg.MajArray {
+		return fmt.Errorf("cbor input should be of type array")
+	}
+
+	if extra > build.BlockMessageLimit {
+		return fmt.Errorf("cbor input had wrong number of fields")
+	}
+
+	if extra > 0 {
+		t.v = make([]uint64, extra)
+	}
+
+	for i := 0; i < int(extra); i++ {
+		maj, extra, err := cr.ReadHeader()
+		if err != nil {
+			return err
+		}
+		if maj != cbg.MajUnsignedInt {
+			return fmt.Errorf("wrong type for uint64 field")
+		}
+		t.v[i] = uint64(extra)
+
+	}
+	return nil
+}
+
+func (t *messageIndices) MarshalCBOR(w io.Writer) error {
+	if t == nil {
+		_, err := w.Write(cbg.CborNull)
+		return err
+	}
+
+	cw := cbg.NewCborWriter(w)
+
+	if len(t.v) > build.BlockMessageLimit {
+		return xerrors.Errorf("Slice value in field v was too long")
+	}
+
+	if err := cw.WriteMajorTypeHeader(cbg.MajArray, uint64(len(t.v))); err != nil {
+		return err
+	}
+	for _, v := range t.v {
+		if err := cw.WriteMajorTypeHeader(cbg.MajUnsignedInt, uint64(v)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/gen/main.go b/gen/main.go
index 0cd3999c38a..942b3ac2c05 100644
--- a/gen/main.go
+++ b/gen/main.go
@@ -92,7 +92,7 @@ func main() {
 	err = gen.WriteTupleEncodersToFile("./chain/exchange/cbor_gen.go", "exchange",
 		exchange.Request{},
 		exchange.Response{},
-		exchange.CompactedMessages{},
+		exchange.CompactedMessagesCBOR{},
 		exchange.BSTipSet{},
 	)
 	if err != nil {