diff --git a/cmd/signer/abihelper.go b/cmd/signer/abihelper.go
index b317b54064..f36e927816 100644
--- a/cmd/signer/abihelper.go
+++ b/cmd/signer/abihelper.go
@@ -17,7 +17,7 @@
 package main
 
 import (
-	"bytes"
+	//	"bytes"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
@@ -26,8 +26,8 @@ import (
 	"github.com/ethereum/go-ethereum/accounts/abi"
 	"github.com/ethereum/go-ethereum/common"
 
+	"bytes"
 	"regexp"
-	"reflect"
 )
 
 type decodedArgument struct {
@@ -79,33 +79,25 @@ func parseCallData(calldata []byte, abidata string) (*decodedCallData, error) {
 		return nil, fmt.Errorf("Failed parsing JSON ABI: %v, abidata: %v", err, abidata)
 	}
 
-	method := abispec.MethodById(sigdata)
-	if method == nil {
-		return nil, fmt.Errorf("Supplied ABI spec does not contain method signature in data: 0x%x", sigdata)
+	method, err := abispec.MethodById(sigdata)
+	if err != nil {
+		return nil, err
 	}
-	var v interface{}
-	method.Inputs.Unpack(v, argdata)
 
-	ref := reflect.ValueOf(v)
-	values := make([]interface{}, ref.NumField())
-
-	for i := 0; i < ref.NumField(); i++ {
-		values[i] = ref.Field(i).Interface()
+	v, err := method.Inputs.UnpackValues(argdata)
+	if err != nil {
+		return nil, err
 	}
-	fmt.Println(values)
-
-
 
 	decoded := decodedCallData{signature: method.Sig(), name: method.Name}
 
-/*
 	for n, argument := range method.Inputs {
 		if err != nil {
 			return nil, fmt.Errorf("Failed to decode argument %d (signature %v): %v", n, method.Sig(), err)
 		} else {
 			decodedArg := decodedArgument{
 				soltype: argument,
-				value: reflect.ValueOf(v,) ,
+				value:   v[n],
 			}
 			decoded.inputs = append(decoded.inputs, decodedArg)
 		}
@@ -115,19 +107,20 @@ func parseCallData(calldata []byte, abidata string) (*decodedCallData, error) {
 	// original data. If we didn't do that, it would e.g. be possible to stuff extra data into the arguments, which
 	// is not detected by merely decoding the data.
 
-
 	var (
-		encoded          []byte
+		encoded []byte
 	)
-	encoded, err = method.Inputs.Pack(v)
+	encoded, err = method.Inputs.PackValues(v)
 
+	if err != nil {
+		return nil, err
+	}
 
-	if !bytes.Equal(encoded, calldata) {
-		exp := common.Bytes2Hex(encoded)
-		was := common.Bytes2Hex(calldata)
+	if !bytes.Equal(encoded, argdata) {
+		was := common.Bytes2Hex(encoded)
+		exp := common.Bytes2Hex(argdata)
 		return nil, fmt.Errorf("WARNING: Supplied data is stuffed with extra data. \nWant %s\nHave %s\nfor method %v", exp, was, method.Sig())
 	}
-*/
 	return &decoded, nil
 }
 
diff --git a/cmd/signer/abihelper_test.go b/cmd/signer/abihelper_test.go
index 04fe553663..d28ad8c298 100644
--- a/cmd/signer/abihelper_test.go
+++ b/cmd/signer/abihelper_test.go
@@ -23,8 +23,93 @@ import (
 
 	"github.com/ethereum/go-ethereum/accounts/abi"
 	"github.com/ethereum/go-ethereum/common"
+	//	"reflect"
+	//	"math/big"
+	"math/big"
+	"reflect"
 )
 
+func verify(t *testing.T, jsondata, calldata string, exp []interface{}) {
+
+	abispec, err := abi.JSON(strings.NewReader(jsondata))
+	if err != nil {
+		t.Fatal(err)
+	}
+	cd := common.Hex2Bytes(calldata)
+	sigdata, argdata := cd[:4], cd[4:]
+	method, err := abispec.MethodById(sigdata)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	data, err := method.Inputs.UnpackValues(argdata)
+
+	if len(data) != len(exp) {
+		t.Fatalf("Mismatched length, expected %d, got %d", len(exp), len(data))
+	}
+	for i, elem := range data {
+		if !reflect.DeepEqual(elem, exp[i]) {
+			t.Fatalf("Unpack error, arg %d, got %v, want %v", i, elem, exp[i])
+		}
+	}
+}
+func TestNewUnpacker(t *testing.T) {
+	type unpackTest struct {
+		jsondata string
+		calldata string
+		exp      []interface{}
+	}
+	testcases := []unpackTest{
+		{ // https://solidity.readthedocs.io/en/develop/abi-spec.html#use-of-dynamic-types
+			`[{"type":"function","name":"f", "inputs":[{"type":"uint256"},{"type":"uint32[]"},{"type":"bytes10"},{"type":"bytes"}]}]`,
+			// 0x123, [0x456, 0x789], "1234567890", "Hello, world!"
+			"8be65246" + "00000000000000000000000000000000000000000000000000000000000001230000000000000000000000000000000000000000000000000000000000000080313233343536373839300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000e0000000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000004560000000000000000000000000000000000000000000000000000000000000789000000000000000000000000000000000000000000000000000000000000000d48656c6c6f2c20776f726c642100000000000000000000000000000000000000",
+			[]interface{}{
+				big.NewInt(0x123),
+				[]uint32{0x456, 0x789},
+				[10]byte{49, 50, 51, 52, 53, 54, 55, 56, 57, 48},
+				common.Hex2Bytes("48656c6c6f2c20776f726c6421"),
+			},
+		}, { // https://github.com/ethereum/wiki/wiki/Ethereum-Contract-ABI#examples
+			`[{"type":"function","name":"sam","inputs":[{"type":"bytes"},{"type":"bool"},{"type":"uint256[]"}]}]`,
+			//  "dave", true and [1,2,3]
+			"a5643bf20000000000000000000000000000000000000000000000000000000000000060000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000a0000000000000000000000000000000000000000000000000000000000000000464617665000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000003000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000003",
+			[]interface{}{
+				[]byte{0x64, 0x61, 0x76, 0x65},
+				true,
+				[]*big.Int{big.NewInt(1), big.NewInt(2), big.NewInt(3)},
+			},
+		}, {
+			`[{"type":"function","name":"send","inputs":[{"type":"uint256"}]}]`,
+			"a52c101e0000000000000000000000000000000000000000000000000000000000000012",
+			[]interface{}{big.NewInt(0x12)},
+		}, {
+			`[{"type":"function","name":"compareAndApprove","inputs":[{"type":"address"},{"type":"uint256"},{"type":"uint256"}]}]`,
+			"751e107900000000000000000000000000000133700000deadbeef00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001",
+			[]interface{}{
+				common.HexToAddress("0x00000133700000deadbeef000000000000000000"),
+				new(big.Int).SetBytes([]byte{0x00}),
+				big.NewInt(0x1),
+			},
+		},
+	}
+	for _, c := range testcases {
+		verify(t, c.jsondata, c.calldata, c.exp)
+	}
+
+}
+
+/*
+func TestReflect(t *testing.T) {
+	a := big.NewInt(0)
+	b := new(big.Int).SetBytes([]byte{0x00})
+	if !reflect.DeepEqual(a, b) {
+		t.Fatalf("Nope, %v != %v", a, b)
+	}
+}
+ */
+
 func TestCalldataDecoding(t *testing.T) {
 
 	// send(uint256)                              : a52c101e
@@ -114,7 +199,11 @@ func TestSelectorUnmarshalling(t *testing.T) {
 			t.Error(err)
 			return
 		}
-		m := abistruct.MethodById(common.Hex2Bytes(id[2:]))
+		m, err := abistruct.MethodById(common.Hex2Bytes(id[2:]))
+		if err != nil {
+			t.Error(err)
+			return
+		}
 		if m.Sig() != selector {
 			t.Errorf("Expected equality: %v != %v", m.Sig(), selector)
 		}