diff --git a/api/cbor_gen.go b/api/cbor_gen.go
index a90ea8b21..8889e6021 100644
--- a/api/cbor_gen.go
+++ b/api/cbor_gen.go
@@ -6,8 +6,8 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/filecoin-project/specs-actors/actors/abi"
-	"github.com/filecoin-project/specs-actors/actors/builtin/paych"
+	abi "github.com/filecoin-project/specs-actors/actors/abi"
+	paych "github.com/filecoin-project/specs-actors/actors/builtin/paych"
 	cbg "github.com/whyrusleeping/cbor-gen"
 	xerrors "golang.org/x/xerrors"
 )
diff --git a/chain/blocksync/cbor_gen.go b/chain/blocksync/cbor_gen.go
index ad8e1de7f..cd43f4a64 100644
--- a/chain/blocksync/cbor_gen.go
+++ b/chain/blocksync/cbor_gen.go
@@ -6,8 +6,8 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/filecoin-project/lotus/chain/types"
-	"github.com/ipfs/go-cid"
+	types "github.com/filecoin-project/lotus/chain/types"
+	cid "github.com/ipfs/go-cid"
 	cbg "github.com/whyrusleeping/cbor-gen"
 	xerrors "golang.org/x/xerrors"
 )
diff --git a/chain/types/cbor_gen.go b/chain/types/cbor_gen.go
index 451971aca..35abf2828 100644
--- a/chain/types/cbor_gen.go
+++ b/chain/types/cbor_gen.go
@@ -6,10 +6,10 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/filecoin-project/specs-actors/actors/abi"
-	"github.com/filecoin-project/specs-actors/actors/crypto"
-	"github.com/filecoin-project/specs-actors/actors/runtime/exitcode"
-	"github.com/ipfs/go-cid"
+	abi "github.com/filecoin-project/specs-actors/actors/abi"
+	crypto "github.com/filecoin-project/specs-actors/actors/crypto"
+	exitcode "github.com/filecoin-project/specs-actors/actors/runtime/exitcode"
+	cid "github.com/ipfs/go-cid"
 	cbg "github.com/whyrusleeping/cbor-gen"
 	xerrors "golang.org/x/xerrors"
 )
@@ -637,15 +637,10 @@ func (t *Message) MarshalCBOR(w io.Writer) error {
 
 	scratch := make([]byte, 9)
 
-	// t.Version (int64) (int64)
-	if t.Version >= 0 {
-		if err := cbg.WriteMajorTypeHeaderBuf(scratch, w, cbg.MajUnsignedInt, uint64(t.Version)); err != nil {
-			return err
-		}
-	} else {
-		if err := cbg.WriteMajorTypeHeaderBuf(scratch, w, cbg.MajNegativeInt, uint64(-t.Version-1)); err != nil {
-			return err
-		}
+	// t.Version (uint64) (uint64)
+
+	if err := cbg.WriteMajorTypeHeaderBuf(scratch, w, cbg.MajUnsignedInt, uint64(t.Version)); err != nil {
+		return err
 	}
 
 	// t.To (address.Address) (struct)
@@ -729,30 +724,19 @@ func (t *Message) UnmarshalCBOR(r io.Reader) error {
 		return fmt.Errorf("cbor input had wrong number of fields")
 	}
 
-	// t.Version (int64) (int64)
+	// t.Version (uint64) (uint64)
+
 	{
-		maj, extra, err := cbg.CborReadHeaderBuf(br, scratch)
-		var extraI int64
+
+		maj, extra, err = cbg.CborReadHeaderBuf(br, scratch)
 		if err != nil {
 			return err
 		}
-		switch maj {
-		case cbg.MajUnsignedInt:
-			extraI = int64(extra)
-			if extraI < 0 {
-				return fmt.Errorf("int64 positive overflow")
-			}
-		case cbg.MajNegativeInt:
-			extraI = int64(extra)
-			if extraI < 0 {
-				return fmt.Errorf("int64 negative oveflow")
-			}
-			extraI = -1 - extraI
-		default:
-			return fmt.Errorf("wrong type for int64 field: %d", maj)
+		if maj != cbg.MajUnsignedInt {
+			return fmt.Errorf("wrong type for uint64 field")
 		}
+		t.Version = uint64(extra)
 
-		t.Version = int64(extraI)
 	}
 	// t.To (address.Address) (struct)
 
diff --git a/chain/types/message.go b/chain/types/message.go
index e9d932ac2..288fcf6d9 100644
--- a/chain/types/message.go
+++ b/chain/types/message.go
@@ -25,7 +25,7 @@ type ChainMsg interface {
 }
 
 type Message struct {
-	Version int64
+	Version uint64
 
 	To   address.Address
 	From address.Address
diff --git a/node/hello/cbor_gen.go b/node/hello/cbor_gen.go
index e28d5c1b4..48d111c6b 100644
--- a/node/hello/cbor_gen.go
+++ b/node/hello/cbor_gen.go
@@ -6,8 +6,8 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/filecoin-project/specs-actors/actors/abi"
-	"github.com/ipfs/go-cid"
+	abi "github.com/filecoin-project/specs-actors/actors/abi"
+	cid "github.com/ipfs/go-cid"
 	cbg "github.com/whyrusleeping/cbor-gen"
 	xerrors "golang.org/x/xerrors"
 )
diff --git a/paychmgr/cbor_gen.go b/paychmgr/cbor_gen.go
index aa86bc106..1a6d17783 100644
--- a/paychmgr/cbor_gen.go
+++ b/paychmgr/cbor_gen.go
@@ -6,8 +6,8 @@ import (
 	"fmt"
 	"io"
 
-	"github.com/filecoin-project/go-address"
-	"github.com/filecoin-project/specs-actors/actors/builtin/paych"
+	address "github.com/filecoin-project/go-address"
+	paych "github.com/filecoin-project/specs-actors/actors/builtin/paych"
 	cbg "github.com/whyrusleeping/cbor-gen"
 	xerrors "golang.org/x/xerrors"
 )