diff --git a/sei-cosmos/types/tx/types.go b/sei-cosmos/types/tx/types.go
index 50ef5e941f..e90428de0f 100644
--- a/sei-cosmos/types/tx/types.go
+++ b/sei-cosmos/types/tx/types.go
@@ -112,6 +112,14 @@ func (t *Tx) ValidateBasic() error {
 		return sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "fee grants are not enabled")
 	}
 
+	// SignerInfos and Signatures are 1:1 (see SetSignatures).
+	if len(authInfo.SignerInfos) != len(sigs) {
+		return sdkerrors.Wrapf(
+			sdkerrors.ErrUnauthorized,
+			"wrong number of SignerInfos; expected %d, got %d", len(sigs), len(authInfo.SignerInfos),
+		)
+	}
+
 	return nil
 }
 
diff --git a/sei-cosmos/x/auth/tx/builder_test.go b/sei-cosmos/x/auth/tx/builder_test.go
index 3ca6d482f0..523af7f618 100644
--- a/sei-cosmos/x/auth/tx/builder_test.go
+++ b/sei-cosmos/x/auth/tx/builder_test.go
@@ -199,6 +199,17 @@ func TestBuilderValidateBasic(t *testing.T) {
 	err = txBuilder.ValidateBasic()
 	require.NoError(t, err)
 
+	// SignerInfos must match Signatures
+	origInfos := txBuilder.tx.AuthInfo.SignerInfos
+	txBuilder.tx.AuthInfo.SignerInfos = append(origInfos, origInfos[0])
+	err = txBuilder.ValidateBasic()
+	require.Error(t, err)
+	_, code, _ = sdkerrors.ABCIInfo(err, false)
+	require.Equal(t, sdkerrors.ErrUnauthorized.ABCICode(), code)
+	txBuilder.tx.AuthInfo.SignerInfos = origInfos
+	err = txBuilder.ValidateBasic()
+	require.NoError(t, err)
+
 	// gas limit too high
 	txBuilder.SetGasLimit(txtypes.MaxGasWanted + 1)
 	err = txBuilder.ValidateBasic()
diff --git a/sei-cosmos/x/auth/tx/sigs.go b/sei-cosmos/x/auth/tx/sigs.go
index 8c133b5ba1..e15c9ddc43 100644
--- a/sei-cosmos/x/auth/tx/sigs.go
+++ b/sei-cosmos/x/auth/tx/sigs.go
@@ -6,6 +6,7 @@ import (
 	"github.com/sei-protocol/sei-chain/sei-cosmos/codec"
 	codectypes "github.com/sei-protocol/sei-chain/sei-cosmos/codec/types"
 	cryptotypes "github.com/sei-protocol/sei-chain/sei-cosmos/crypto/types"
+	sdkerrors "github.com/sei-protocol/sei-chain/sei-cosmos/types/errors"
 	"github.com/sei-protocol/sei-chain/sei-cosmos/types/tx"
 	"github.com/sei-protocol/sei-chain/sei-cosmos/types/tx/signing"
 )
@@ -70,6 +71,11 @@ func ModeInfoAndSigToSignatureData(modeInfo *tx.ModeInfo, sig []byte) (signing.S
 		if err != nil {
 			return nil, err
 		}
+		// ModeInfos and nested signatures are 1:1 (see SignatureDataToModeInfoAndSig).
+		if len(multi.ModeInfos) != len(sigs) {
+			return nil, sdkerrors.Wrapf(sdkerrors.ErrTxDecode,
+				"invalid multisig: %d mode infos, %d signatures", len(multi.ModeInfos), len(sigs))
+		}
 
 		sigv2s := make([]signing.SignatureData, len(sigs))
 		for i, mi := range multi.ModeInfos {
@@ -85,7 +91,7 @@ func ModeInfoAndSigToSignatureData(modeInfo *tx.ModeInfo, sig []byte) (signing.S
 		}, nil
 
 	default:
-		panic(fmt.Errorf("unexpected ModeInfo data type %T", modeInfo))
+		return nil, sdkerrors.Wrapf(sdkerrors.ErrTxDecode, "unexpected ModeInfo data type %T", modeInfo)
 	}
 }
 
diff --git a/sei-cosmos/x/auth/tx/sigs_test.go b/sei-cosmos/x/auth/tx/sigs_test.go
index 619f727572..5dd1e03362 100644
--- a/sei-cosmos/x/auth/tx/sigs_test.go
+++ b/sei-cosmos/x/auth/tx/sigs_test.go
@@ -5,9 +5,12 @@ import (
 
 	"github.com/stretchr/testify/require"
 
-	"github.com/sei-protocol/sei-chain/sei-cosmos/crypto/types"
-
+	cryptotypes "github.com/sei-protocol/sei-chain/sei-cosmos/crypto/types"
+	"github.com/sei-protocol/sei-chain/sei-cosmos/crypto/types/multisig"
 	"github.com/sei-protocol/sei-chain/sei-cosmos/testutil/testdata"
+	sdkerrors "github.com/sei-protocol/sei-chain/sei-cosmos/types/errors"
+	txtypes "github.com/sei-protocol/sei-chain/sei-cosmos/types/tx"
+	"github.com/sei-protocol/sei-chain/sei-cosmos/types/tx/signing"
 )
 
 func TestDecodeMultisignatures(t *testing.T) {
@@ -27,7 +30,7 @@ func TestDecodeMultisignatures(t *testing.T) {
 	_, err = decodeMultisignatures(bz)
 	require.Error(t, err)
 
-	goodMultisig := types.MultiSignature{
+	goodMultisig := cryptotypes.MultiSignature{
 		Signatures: testSigs,
 	}
 	bz, err = goodMultisig.Marshal()
@@ -38,3 +41,64 @@ func TestDecodeMultisignatures(t *testing.T) {
 
 	require.Equal(t, testSigs, decodedSigs)
 }
+
+func TestModeInfoAndSigToSignatureData(t *testing.T) {
+	single := &signing.SingleSignatureData{
+		SignMode:  signing.SignMode_SIGN_MODE_DIRECT,
+		Signature: []byte("a"),
+	}
+
+	// Nested Multi ModeInfo exercises the recursive decode path.
+	inner := multisig.NewMultisig(2)
+	multisig.AddSignature(inner, single, 0)
+	outer := multisig.NewMultisig(2)
+	multisig.AddSignature(outer, &signing.SingleSignatureData{
+		SignMode:  signing.SignMode_SIGN_MODE_DIRECT,
+		Signature: []byte("b"),
+	}, 0)
+	multisig.AddSignature(outer, inner, 1)
+	modeInfo, raw := SignatureDataToModeInfoAndSig(outer)
+	got, err := ModeInfoAndSigToSignatureData(modeInfo, raw)
+	require.NoError(t, err)
+	require.Equal(t, outer, got)
+
+	mi := &txtypes.ModeInfo{Sum: &txtypes.ModeInfo_Single_{
+		Single: &txtypes.ModeInfo_Single{Mode: signing.SignMode_SIGN_MODE_DIRECT},
+	}}
+	bad := &txtypes.ModeInfo{Sum: &txtypes.ModeInfo_Multi_{
+		Multi: &txtypes.ModeInfo_Multi{
+			Bitarray:  cryptotypes.NewCompactBitArray(2),
+			ModeInfos: []*txtypes.ModeInfo{mi, mi},
+		},
+	}}
+
+	// fewer nested sigs than ModeInfos must error
+	rawShort, err := (&cryptotypes.MultiSignature{Signatures: [][]byte{[]byte("a")}}).Marshal()
+	require.NoError(t, err)
+	_, err = ModeInfoAndSigToSignatureData(bad, rawShort)
+	require.ErrorIs(t, err, sdkerrors.ErrTxDecode)
+
+	// more nested sigs than ModeInfos must error
+	rawLong, err := (&cryptotypes.MultiSignature{Signatures: [][]byte{[]byte("a"), []byte("b"), []byte("c")}}).Marshal()
+	require.NoError(t, err)
+	_, err = ModeInfoAndSigToSignatureData(bad, rawLong)
+	require.ErrorIs(t, err, sdkerrors.ErrTxDecode)
+
+	// mismatch inside nested Multi ModeInfo must error on the recursive call
+	innerShort, err := (&cryptotypes.MultiSignature{Signatures: [][]byte{[]byte("a")}}).Marshal()
+	require.NoError(t, err)
+	rawNested, err := (&cryptotypes.MultiSignature{Signatures: [][]byte{[]byte("b"), innerShort}}).Marshal()
+	require.NoError(t, err)
+	nestedBad := &txtypes.ModeInfo{Sum: &txtypes.ModeInfo_Multi_{
+		Multi: &txtypes.ModeInfo_Multi{
+			Bitarray:  cryptotypes.NewCompactBitArray(2),
+			ModeInfos: []*txtypes.ModeInfo{mi, bad},
+		},
+	}}
+	_, err = ModeInfoAndSigToSignatureData(nestedBad, rawNested)
+	require.ErrorIs(t, err, sdkerrors.ErrTxDecode)
+
+	// non-nil ModeInfo with unset Sum oneof must error (not panic)
+	_, err = ModeInfoAndSigToSignatureData(&txtypes.ModeInfo{}, []byte("a"))
+	require.ErrorIs(t, err, sdkerrors.ErrTxDecode)
+}