diff --git a/pkg/smartcontract/context/context.go b/pkg/smartcontract/context/context.go
index 16fc0b424..b22c9cb22 100644
--- a/pkg/smartcontract/context/context.go
+++ b/pkg/smartcontract/context/context.go
@@ -135,7 +135,7 @@ func (c *ParameterContext) getItemForContract(ctr *wallet.Contract) *Item {
 		params[i].Type = ctr.Parameters[i].Type
 	}
 	item := &Item{
-		Script:     h,
+		Script:     ctr.Script,
 		Parameters: params,
 		Signatures: make(map[string][]byte),
 	}
diff --git a/pkg/smartcontract/context/context_test.go b/pkg/smartcontract/context/context_test.go
index 8c389e97c..2be84eb03 100644
--- a/pkg/smartcontract/context/context_test.go
+++ b/pkg/smartcontract/context/context_test.go
@@ -2,6 +2,7 @@ package context
 
 import (
 	"encoding/hex"
+	"encoding/json"
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/internal/testserdes"
@@ -131,7 +132,7 @@ func TestParameterContext_MarshalJSON(t *testing.T) {
 		Verifiable: tx,
 		Items: map[util.Uint160]*Item{
 			priv.GetScriptHash(): {
-				Script: priv.GetScriptHash(),
+				Script: priv.PublicKey().GetVerificationScript(),
 				Parameters: []smartcontract.Parameter{{
 					Type:  smartcontract.SignatureType,
 					Value: sign,
@@ -144,6 +145,22 @@ func TestParameterContext_MarshalJSON(t *testing.T) {
 	}
 
 	testserdes.MarshalUnmarshalJSON(t, expected, new(ParameterContext))
+
+	t.Run("invalid script", func(t *testing.T) {
+		js := `{
+ 			"script": "AQID",
+ 			"parameters": [
+  				{
+   					"type": "Signature",
+   					"value": "QfOZLLqjMyPWMzRxMAKw7fcd8leLcpwiiTV2pUyC0pth/y7Iw7o7WzNpxeAJm5bmExmlF7g5pMhXz1xVT6KK3g=="
+  				}
+			],
+ 			"signatures": {
+				"025c210bde738e0e646929ee04ec2ccb42a700356083f55386b5347b9b725c10b9": "a6c6d8a2334791888df559419f07209ee39e2f20688af8cc38010854b98abf77194e37f173bbc86b77dce4afa8ce3ae5170dd346b5265bcb9b723d83299a6f0f",
+  				"035d4da640b3a39f19ed88855aeddd97725422b4230ccae56bd5544419d0056ea9": "058e577f23395f382194eebb83f66bb8903c8f3c5b6afd759c20f2518466124dcd9cbccfc029a42e9a7d5a3a060b091edc73dcac949fd894d7a9d10678296ac6"
+		}`
+		require.Error(t, json.Unmarshal([]byte(js), new(ParameterContext)))
+	})
 }
 
 func getPrivateKeys(t *testing.T, n int) ([]*keys.PrivateKey, []*keys.PublicKey) {
diff --git a/pkg/smartcontract/context/item.go b/pkg/smartcontract/context/item.go
index fcbb3e9fc..2b8a3dc57 100644
--- a/pkg/smartcontract/context/item.go
+++ b/pkg/smartcontract/context/item.go
@@ -1,23 +1,23 @@
 package context
 
 import (
+	"encoding/base64"
 	"encoding/hex"
 	"encoding/json"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
-	"github.com/nspcc-dev/neo-go/pkg/util"
 )
 
 // Item represents a transaction context item.
 type Item struct {
-	Script     util.Uint160
+	Script     []byte
 	Parameters []smartcontract.Parameter
 	Signatures map[string][]byte
 }
 
 type itemAux struct {
-	Script     util.Uint160              `json:"script"`
+	Script     string                    `json:"script"`
 	Parameters []smartcontract.Parameter `json:"parameters"`
 	Signatures map[string]string         `json:"signatures"`
 }
@@ -36,7 +36,7 @@ func (it *Item) AddSignature(pub *keys.PublicKey, sig []byte) {
 // MarshalJSON implements json.Marshaler interface.
 func (it Item) MarshalJSON() ([]byte, error) {
 	ci := itemAux{
-		Script:     it.Script,
+		Script:     base64.StdEncoding.EncodeToString(it.Script),
 		Parameters: it.Parameters,
 		Signatures: make(map[string]string, len(it.Signatures)),
 	}
@@ -55,6 +55,11 @@ func (it *Item) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
+	script, err := base64.StdEncoding.DecodeString(ci.Script)
+	if err != nil {
+		return err
+	}
+
 	sigs := make(map[string][]byte, len(ci.Signatures))
 	for keyHex, sigHex := range ci.Signatures {
 		_, err := keys.NewPublicKeyFromString(keyHex)
@@ -69,7 +74,7 @@ func (it *Item) UnmarshalJSON(data []byte) error {
 	}
 
 	it.Signatures = sigs
-	it.Script = ci.Script
+	it.Script = script
 	it.Parameters = ci.Parameters
 	return nil
 }
diff --git a/pkg/smartcontract/context/item_test.go b/pkg/smartcontract/context/item_test.go
index ca29fc897..21108aa4d 100644
--- a/pkg/smartcontract/context/item_test.go
+++ b/pkg/smartcontract/context/item_test.go
@@ -8,7 +8,6 @@ import (
 	"github.com/nspcc-dev/neo-go/internal/testserdes"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
-	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/stretchr/testify/require"
 )
 
@@ -41,7 +40,7 @@ func TestContextItem_MarshalJSON(t *testing.T) {
 	require.NoError(t, err)
 
 	expected := &Item{
-		Script: util.Uint160{1, 2, 3},
+		Script: []byte{1, 2, 3},
 		Parameters: []smartcontract.Parameter{{
 			Type:  smartcontract.SignatureType,
 			Value: random.Bytes(64),