diff --git a/pkg/smartcontract/param_context.go b/pkg/smartcontract/param_context.go
index 147e00c9f..14f953f6b 100644
--- a/pkg/smartcontract/param_context.go
+++ b/pkg/smartcontract/param_context.go
@@ -66,7 +66,11 @@ func (p *Parameter) MarshalJSON() ([]byte, error) {
 	case BoolType, IntegerType, StringType, Hash256Type, Hash160Type:
 		resultRawValue, resultErr = json.Marshal(p.Value)
 	case PublicKeyType, ByteArrayType, SignatureType:
-		resultRawValue, resultErr = json.Marshal(hex.EncodeToString(p.Value.([]byte)))
+		if p.Value == nil {
+			resultRawValue = []byte("null")
+		} else {
+			resultRawValue, resultErr = json.Marshal(hex.EncodeToString(p.Value.([]byte)))
+		}
 	case ArrayType:
 		var value = make([]rawParameter, 0)
 		for _, parameter := range p.Value.([]Parameter) {
diff --git a/pkg/smartcontract/param_context_test.go b/pkg/smartcontract/param_context_test.go
index b6870e8eb..565ca95d6 100644
--- a/pkg/smartcontract/param_context_test.go
+++ b/pkg/smartcontract/param_context_test.go
@@ -30,6 +30,10 @@ var marshalJSONTestCases = []struct {
 		input:  Parameter{Type: ByteArrayType, Value: []byte{0x01, 0x02, 0x03}},
 		result: `{"type":"ByteArray","value":"010203"}`,
 	},
+	{
+		input:  Parameter{Type: ByteArrayType},
+		result: `{"type":"ByteArray","value":null}`,
+	},
 	{
 		input: Parameter{
 			Type:  PublicKeyType,
diff --git a/pkg/smartcontract/param_type.go b/pkg/smartcontract/param_type.go
index ed00bb112..c0e465afb 100644
--- a/pkg/smartcontract/param_type.go
+++ b/pkg/smartcontract/param_type.go
@@ -9,6 +9,7 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
 	"github.com/nspcc-dev/neo-go/pkg/io"
+	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/pkg/errors"
 )
 
@@ -169,7 +170,7 @@ func adjustValToType(typ ParamType, val string) (interface{}, error) {
 		if len(b) != 64 {
 			return nil, errors.New("not a signature")
 		}
-		return val, nil
+		return b, nil
 	case BoolType:
 		switch val {
 		case "true":
@@ -184,37 +185,31 @@ func adjustValToType(typ ParamType, val string) (interface{}, error) {
 	case Hash160Type:
 		u, err := address.StringToUint160(val)
 		if err == nil {
-			return hex.EncodeToString(u.BytesBE()), nil
+			return u, nil
 		}
-		b, err := hex.DecodeString(val)
+		u, err = util.Uint160DecodeStringLE(val)
 		if err != nil {
 			return nil, err
 		}
-		if len(b) != 20 {
-			return nil, errors.New("not a hash160")
-		}
-		return val, nil
+		return u, nil
 	case Hash256Type:
+		u, err := util.Uint256DecodeStringLE(val)
+		if err != nil {
+			return nil, err
+		}
+		return u, nil
+	case ByteArrayType:
 		b, err := hex.DecodeString(val)
 		if err != nil {
 			return nil, err
 		}
-		if len(b) != 32 {
-			return nil, errors.New("not a hash256")
-		}
-		return val, nil
-	case ByteArrayType:
-		_, err := hex.DecodeString(val)
-		if err != nil {
-			return nil, err
-		}
-		return val, nil
+		return b, nil
 	case PublicKeyType:
-		_, err := keys.NewPublicKeyFromString(val)
+		pub, err := keys.NewPublicKeyFromString(val)
 		if err != nil {
 			return nil, err
 		}
-		return val, nil
+		return pub.Bytes(), nil
 	case StringType:
 		return val, nil
 	default:
diff --git a/pkg/smartcontract/param_type_test.go b/pkg/smartcontract/param_type_test.go
index 629f1eca5..2130ed413 100644
--- a/pkg/smartcontract/param_type_test.go
+++ b/pkg/smartcontract/param_type_test.go
@@ -1,8 +1,10 @@
 package smartcontract
 
 import (
+	"encoding/hex"
 	"testing"
 
+	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -151,7 +153,7 @@ func TestAdjustValToType(t *testing.T) {
 	}{{
 		typ: SignatureType,
 		val: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7c56f33fc6ecfcd0c225c4ab356fee59390af8560be0e930faebe74a6daff7c9b",
-		out: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7c56f33fc6ecfcd0c225c4ab356fee59390af8560be0e930faebe74a6daff7c9b",
+		out: mustHex("602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7c56f33fc6ecfcd0c225c4ab356fee59390af8560be0e930faebe74a6daff7c9b"),
 	}, {
 		typ: SignatureType,
 		val: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7c56f33fc6ecfcd0c225c4ab356fee59390af8560be0e930faebe74a6daff7c",
@@ -199,11 +201,17 @@ func TestAdjustValToType(t *testing.T) {
 	}, {
 		typ: Hash160Type,
 		val: "AK2nJJpJr6o664CWJKi1QRXjqeic2zRp8y",
-		out: "23ba2703c53263e8d6e522dc32203339dcd8eee9",
+		out: util.Uint160{
+			0x23, 0xba, 0x27, 0x3, 0xc5, 0x32, 0x63, 0xe8, 0xd6, 0xe5,
+			0x22, 0xdc, 0x32, 0x20, 0x33, 0x39, 0xdc, 0xd8, 0xee, 0xe9,
+		},
 	}, {
 		typ: Hash160Type,
 		val: "50befd26fdf6e4d957c11e078b24ebce6291456f",
-		out: "50befd26fdf6e4d957c11e078b24ebce6291456f",
+		out: util.Uint160{
+			0x6f, 0x45, 0x91, 0x62, 0xce, 0xeb, 0x24, 0x8b, 0x7, 0x1e,
+			0xc1, 0x57, 0xd9, 0xe4, 0xf6, 0xfd, 0x26, 0xfd, 0xbe, 0x50,
+		},
 	}, {
 		typ: Hash160Type,
 		val: "befd26fdf6e4d957c11e078b24ebce6291456f",
@@ -215,7 +223,10 @@ func TestAdjustValToType(t *testing.T) {
 	}, {
 		typ: Hash256Type,
 		val: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7",
-		out: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7",
+		out: util.Uint256{
+			0xe7, 0x2d, 0x28, 0x69, 0x79, 0xee, 0x6c, 0xb1, 0xb7, 0xe6, 0x5d, 0xfd, 0xdf, 0xb2, 0xe3, 0x84,
+			0x10, 0xb, 0x8d, 0x14, 0x8e, 0x77, 0x58, 0xde, 0x42, 0xe4, 0x16, 0x8b, 0x71, 0x79, 0x2c, 0x60,
+		},
 	}, {
 		typ: Hash256Type,
 		val: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282d",
@@ -227,15 +238,15 @@ func TestAdjustValToType(t *testing.T) {
 	}, {
 		typ: ByteArrayType,
 		val: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282d",
-		out: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282d",
+		out: mustHex("602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282d"),
 	}, {
 		typ: ByteArrayType,
 		val: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7",
-		out: "602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7",
+		out: mustHex("602c79718b16e442de58778e148d0b1084e3b2dffd5de6b7b16cee7969282de7"),
 	}, {
 		typ: ByteArrayType,
 		val: "50befd26fdf6e4d957c11e078b24ebce6291456f",
-		out: "50befd26fdf6e4d957c11e078b24ebce6291456f",
+		out: mustHex("50befd26fdf6e4d957c11e078b24ebce6291456f"),
 	}, {
 		typ: ByteArrayType,
 		val: "AK2nJJpJr6o664CWJKi1QRXjqeic2zRp8y",
@@ -247,11 +258,11 @@ func TestAdjustValToType(t *testing.T) {
 	}, {
 		typ: ByteArrayType,
 		val: "ab",
-		out: "ab",
+		out: mustHex("ab"),
 	}, {
 		typ: PublicKeyType,
 		val: "03b209fd4f53a7170ea4444e0cb0a6bb6a53c2bd016926989cf85f9b0fba17a70c",
-		out: "03b209fd4f53a7170ea4444e0cb0a6bb6a53c2bd016926989cf85f9b0fba17a70c",
+		out: mustHex("03b209fd4f53a7170ea4444e0cb0a6bb6a53c2bd016926989cf85f9b0fba17a70c"),
 	}, {
 		typ: PublicKeyType,
 		val: "01b209fd4f53a7170ea4444e0cb0a6bb6a53c2bd016926989cf85f9b0fba17a70c",
@@ -296,3 +307,11 @@ func TestAdjustValToType(t *testing.T) {
 		}
 	}
 }
+
+func mustHex(s string) []byte {
+	b, err := hex.DecodeString(s)
+	if err != nil {
+		panic(err)
+	}
+	return b
+}