diff --git a/client/v2/CHANGELOG.md b/client/v2/CHANGELOG.md
index a3702845c575..8bd7877b448a 100644
--- a/client/v2/CHANGELOG.md
+++ b/client/v2/CHANGELOG.md
@@ -53,6 +53,10 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 * [#17709](https://github.com/cosmos/cosmos-sdk/pull/17709) Address codecs have been removed from `autocli.AppOptions` and `flag.Builder`. Instead client/v2 uses the address codecs present in the context (introduced in [#17503](https://github.com/cosmos/cosmos-sdk/pull/17503)).
 
+### Bug Fixes
+
+* [#21853](https://github.com/cosmos/cosmos-sdk/pull/21853) Fix `*big.Int` unmarshalling in txs.
+
 ## [v2.0.0-beta.5] - 2024-09-18
 
 ### Improvements
diff --git a/client/v2/autocli/flag/builder.go b/client/v2/autocli/flag/builder.go
index 6ff325c53bdb..bdd42634dd35 100644
--- a/client/v2/autocli/flag/builder.go
+++ b/client/v2/autocli/flag/builder.go
@@ -26,6 +26,7 @@ const (
 	ValidatorAddressStringScalarType = "cosmos.ValidatorAddressString"
 	ConsensusAddressStringScalarType = "cosmos.ConsensusAddressString"
 	PubkeyScalarType                 = "cosmos.Pubkey"
+	DecScalarType                    = "cosmos.Dec"
 )
 
 // Builder manages options for building pflag flags for protobuf messages.
@@ -67,6 +68,7 @@ func (b *Builder) init() {
 		b.scalarFlagTypes[ValidatorAddressStringScalarType] = validatorAddressStringType{}
 		b.scalarFlagTypes[ConsensusAddressStringScalarType] = consensusAddressStringType{}
 		b.scalarFlagTypes[PubkeyScalarType] = pubkeyType{}
+		b.scalarFlagTypes[DecScalarType] = decType{}
 	}
 }
 
diff --git a/client/v2/autocli/flag/legacy_dec.go b/client/v2/autocli/flag/legacy_dec.go
new file mode 100644
index 000000000000..073afa94f1f5
--- /dev/null
+++ b/client/v2/autocli/flag/legacy_dec.go
@@ -0,0 +1,48 @@
+package flag
+
+import (
+	"context"
+
+	"google.golang.org/protobuf/reflect/protoreflect"
+
+	"cosmossdk.io/math"
+)
+
+type decType struct{}
+
+func (a decType) NewValue(_ *context.Context, _ *Builder) Value {
+	return &decValue{}
+}
+
+func (a decType) DefaultValue() string {
+	return "0"
+}
+
+type decValue struct {
+	value string
+}
+
+func (a decValue) Get(protoreflect.Value) (protoreflect.Value, error) {
+	return protoreflect.ValueOf(a.value), nil
+}
+
+func (a decValue) String() string {
+	return a.value
+}
+
+func (a *decValue) Set(s string) error {
+	dec, err := math.LegacyNewDecFromStr(s)
+	if err != nil {
+		return err
+	}
+
+	// we need to convert from float representation to non-float representation using default precision
+	// 0.5 -> 500000000000000000
+	a.value = dec.BigInt().String()
+
+	return nil
+}
+
+func (a decValue) Type() string {
+	return "cosmos.Dec"
+}
diff --git a/x/auth/tx/builder.go b/x/auth/tx/builder.go
index 423bca3a0870..2b1c866e8e0a 100644
--- a/x/auth/tx/builder.go
+++ b/x/auth/tx/builder.go
@@ -112,7 +112,7 @@ var marshalOption = proto.MarshalOptions{
 func (w *builder) getTx() (*gogoTxWrapper, error) {
 	anyMsgs, err := msgsV1toAnyV2(w.msgs)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("unable to convert messages: %w", err)
 	}
 	body := &txv1beta1.TxBody{
 		Messages:                    anyMsgs,
@@ -136,12 +136,12 @@ func (w *builder) getTx() (*gogoTxWrapper, error) {
 
 	bodyBytes, err := marshalOption.Marshal(body)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("unable to marshal body: %w", err)
 	}
 
 	authInfoBytes, err := marshalOption.Marshal(authInfo)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("unable to marshal auth info: %w", err)
 	}
 
 	txRawBytes, err := marshalOption.Marshal(&txv1beta1.TxRaw{
@@ -150,12 +150,12 @@ func (w *builder) getTx() (*gogoTxWrapper, error) {
 		Signatures:    w.signatures,
 	})
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("unable to marshal tx raw: %w", err)
 	}
 
 	decodedTx, err := w.decoder.Decode(txRawBytes)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("unable to decode tx: %w", err)
 	}
 
 	return newWrapperFromDecodedTx(w.addressCodec, w.codec, decodedTx)
diff --git a/x/tx/decode/decode.go b/x/tx/decode/decode.go
index 994d54cf488b..bf4f3a54f31f 100644
--- a/x/tx/decode/decode.go
+++ b/x/tx/decode/decode.go
@@ -84,7 +84,7 @@ func (d *Decoder) Decode(txBytes []byte) (*DecodedTx, error) {
 
 	err = proto.Unmarshal(txBytes, &raw)
 	if err != nil {
-		return nil, err
+		return nil, errorsmod.Wrap(ErrTxDecode, err.Error())
 	}
 
 	var body v1beta1.TxBody
@@ -136,7 +136,7 @@ func (d *Decoder) Decode(txBytes []byte) (*DecodedTx, error) {
 		dynamicMsg := dynamicpb.NewMessageType(msgDesc.(protoreflect.MessageDescriptor)).New().Interface()
 		err = anyMsg.UnmarshalTo(dynamicMsg)
 		if err != nil {
-			return nil, err
+			return nil, errorsmod.Wrap(ErrTxDecode, fmt.Sprintf("cannot unmarshal Any message: %v", err))
 		}
 		dynamicMsgs = append(dynamicMsgs, dynamicMsg)
 
@@ -148,7 +148,7 @@ func (d *Decoder) Decode(txBytes []byte) (*DecodedTx, error) {
 		msg := reflect.New(gogoType.Elem()).Interface().(gogoproto.Message)
 		err = d.codec.Unmarshal(anyMsg.Value, msg)
 		if err != nil {
-			return nil, err
+			return nil, errorsmod.Wrap(ErrTxDecode, err.Error())
 		}
 		msgs = append(msgs, msg)