diff --git a/pkg/core/interop_system.go b/pkg/core/interop_system.go
index e7578180f..e83e3880f 100644
--- a/pkg/core/interop_system.go
+++ b/pkg/core/interop_system.go
@@ -219,8 +219,9 @@ func storageFind(ic *interop.Context) error {
 // given m and a set of public keys.
 func contractCreateMultisigAccount(ic *interop.Context) error {
 	m := ic.VM.Estack().Pop().BigInt()
-	if !m.IsInt64() || m.Int64() > math.MaxInt32 {
-		return errors.New("m should fit int32")
+	mu64 := m.Uint64()
+	if !m.IsUint64() || mu64 > math.MaxInt32 {
+		return errors.New("m must be positive and fit int32")
 	}
 	arr := ic.VM.Estack().Pop().Array()
 	pubs := make(keys.PublicKeys, len(arr))
@@ -231,7 +232,7 @@ func contractCreateMultisigAccount(ic *interop.Context) error {
 		}
 		pubs[i] = p
 	}
-	script, err := smartcontract.CreateMultiSigRedeemScript(int(m.Int64()), pubs)
+	script, err := smartcontract.CreateMultiSigRedeemScript(int(mu64), pubs)
 	if err != nil {
 		return err
 	}
diff --git a/pkg/core/native/ledger.go b/pkg/core/native/ledger.go
index ad9b68185..0abc315ab 100644
--- a/pkg/core/native/ledger.go
+++ b/pkg/core/native/ledger.go
@@ -157,9 +157,9 @@ func isTraceableBlock(bc blockchainer.Blockchainer, index uint32) bool {
 // be called within VM context, so it panics if anything goes wrong.
 func getBlockHashFromItem(bc blockchainer.Blockchainer, item stackitem.Item) util.Uint256 {
 	bigindex, err := item.TryInteger()
-	if err == nil && bigindex.IsInt64() {
-		index := bigindex.Int64()
-		if index < 0 || index > math.MaxUint32 {
+	if err == nil && bigindex.IsUint64() {
+		index := bigindex.Uint64()
+		if index > math.MaxUint32 {
 			panic("bad block index")
 		}
 		if uint32(index) > bc.BlockHeight() {
diff --git a/pkg/core/native/native_nep17.go b/pkg/core/native/native_nep17.go
index 0bf47a615..3a6612121 100644
--- a/pkg/core/native/native_nep17.go
+++ b/pkg/core/native/native_nep17.go
@@ -343,12 +343,12 @@ func toUint160(s stackitem.Item) util.Uint160 {
 
 func toUint32(s stackitem.Item) uint32 {
 	bigInt := toBigInt(s)
-	if !bigInt.IsInt64() {
-		panic("bigint is not an int64")
+	if !bigInt.IsUint64() {
+		panic("bigint is not an uint64")
 	}
-	int64Value := bigInt.Int64()
-	if int64Value < 0 || int64Value > math.MaxUint32 {
+	uint64Value := bigInt.Uint64()
+	if uint64Value > math.MaxUint32 {
 		panic("bigint does not fit into uint32")
 	}
-	return uint32(int64Value)
+	return uint32(uint64Value)
 }
diff --git a/pkg/core/state/contract.go b/pkg/core/state/contract.go
index b5a526cbc..9d7cf8514 100644
--- a/pkg/core/state/contract.go
+++ b/pkg/core/state/contract.go
@@ -73,10 +73,10 @@ func (c *Contract) FromStackItem(item stackitem.Item) error {
 	if !ok {
 		return errors.New("UpdateCounter is not an integer")
 	}
-	if !bi.IsInt64() || bi.Int64() > math.MaxUint16 || bi.Int64() < 0 {
+	if !bi.IsUint64() || bi.Uint64() > math.MaxUint16 {
 		return errors.New("UpdateCounter not in uint16 range")
 	}
-	c.UpdateCounter = uint16(bi.Int64())
+	c.UpdateCounter = uint16(bi.Uint64())
 	bytes, err := arr[2].TryBytes()
 	if err != nil {
 		return err
diff --git a/pkg/core/state/deposit.go b/pkg/core/state/deposit.go
index 3efd76d7a..59c97fe54 100644
--- a/pkg/core/state/deposit.go
+++ b/pkg/core/state/deposit.go
@@ -41,11 +41,11 @@ func (d *Deposit) FromStackItem(it stackitem.Item) error {
 	if err != nil {
 		return fmt.Errorf("invalid till: %w", err)
 	}
-	ti64 := till.Int64()
-	if !till.IsInt64() || ti64 > math.MaxUint32 || ti64 < 0 {
+	tiu64 := till.Uint64()
+	if !till.IsUint64() || tiu64 > math.MaxUint32 {
 		return errors.New("wrong till value")
 	}
 	d.Amount = amount
-	d.Till = uint32(ti64)
+	d.Till = uint32(tiu64)
 	return nil
 }
diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 0d65f3bf2..2f1d57d1d 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -918,7 +918,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 	case opcode.POW:
 		exp := v.estack.Pop().BigInt()
 		a := v.estack.Pop().BigInt()
-		if ei := exp.Int64(); !exp.IsInt64() || ei > maxSHLArg || ei < 0 {
+		if ei := exp.Uint64(); !exp.IsUint64() || ei > maxSHLArg {
 			panic("invalid exponent")
 		}
 		v.estack.PushVal(new(big.Int).Exp(a, exp, nil))