diff --git a/api/swagger.json b/api/swagger.json
index c6b4bd9d..0ee1a506 100644
--- a/api/swagger.json
+++ b/api/swagger.json
@@ -2595,9 +2595,9 @@
       "minimum": 0,
       "x-go-type": {
         "import": {
-          "package": "math/big"
+          "package": "github.com/aeternity/aepp-sdk-go/utils"
         },
-        "type": "Int"
+        "type": "BigInt"
       }
     },
     "Balance": {
@@ -2605,9 +2605,9 @@
       "minimum": 0,
       "x-go-type": {
         "import": {
-          "package": "math/big"
+          "package": "github.com/aeternity/aepp-sdk-go/utils"
         },
-        "type": "Int"
+        "type": "BigInt"
       }
     },
     "EncodedHash": {
@@ -2618,9 +2618,9 @@
       "minimum": 0,
       "x-go-type": {
         "import": {
-          "package": "math/big"
+          "package": "github.com/aeternity/aepp-sdk-go/utils"
         },
-        "type": "Int"
+        "type": "BigInt"
       }
     },
     "Pow": {
diff --git a/generated/models/account.go b/generated/models/account.go
index 368cfd2f..7afe4309 100644
--- a/generated/models/account.go
+++ b/generated/models/account.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // Account account
@@ -21,7 +21,7 @@ type Account struct {
 
 	// Balance
 	// Required: true
-	Balance big.Int `json:"balance"`
+	Balance utils.BigInt `json:"balance"`
 
 	// Public key
 	// Required: true
diff --git a/generated/models/channel.go b/generated/models/channel.go
index a30f776d..4a655c39 100644
--- a/generated/models/channel.go
+++ b/generated/models/channel.go
@@ -14,7 +14,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // Channel channel
@@ -23,11 +23,11 @@ type Channel struct {
 
 	// channel amount
 	// Required: true
-	ChannelAmount big.Int `json:"channel_amount"`
+	ChannelAmount utils.BigInt `json:"channel_amount"`
 
 	// channel reserve
 	// Required: true
-	ChannelReserve big.Int `json:"channel_reserve"`
+	ChannelReserve utils.BigInt `json:"channel_reserve"`
 
 	// delegate ids
 	// Required: true
@@ -39,7 +39,7 @@ type Channel struct {
 
 	// initiator amount
 	// Required: true
-	InitiatorAmount big.Int `json:"initiator_amount"`
+	InitiatorAmount utils.BigInt `json:"initiator_amount"`
 
 	// initiator id
 	// Required: true
@@ -56,7 +56,7 @@ type Channel struct {
 
 	// responder amount
 	// Required: true
-	ResponderAmount big.Int `json:"responder_amount"`
+	ResponderAmount utils.BigInt `json:"responder_amount"`
 
 	// responder id
 	// Required: true
diff --git a/generated/models/channel_close_mutual_tx.go b/generated/models/channel_close_mutual_tx.go
index c32a0f7e..4843400f 100644
--- a/generated/models/channel_close_mutual_tx.go
+++ b/generated/models/channel_close_mutual_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelCloseMutualTx channel close mutual tx
@@ -25,7 +25,7 @@ type ChannelCloseMutualTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// from id
 	// Required: true
@@ -33,7 +33,7 @@ type ChannelCloseMutualTx struct {
 
 	// initiator amount final
 	// Required: true
-	InitiatorAmountFinal big.Int `json:"initiator_amount_final"`
+	InitiatorAmountFinal utils.BigInt `json:"initiator_amount_final"`
 
 	// nonce
 	// Required: true
@@ -42,7 +42,7 @@ type ChannelCloseMutualTx struct {
 
 	// responder amount final
 	// Required: true
-	ResponderAmountFinal big.Int `json:"responder_amount_final"`
+	ResponderAmountFinal utils.BigInt `json:"responder_amount_final"`
 
 	// ttl
 	// Minimum: 0
diff --git a/generated/models/channel_close_solo_tx.go b/generated/models/channel_close_solo_tx.go
index d4fe7017..bc86457b 100644
--- a/generated/models/channel_close_solo_tx.go
+++ b/generated/models/channel_close_solo_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelCloseSoloTx channel close solo tx
@@ -25,7 +25,7 @@ type ChannelCloseSoloTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// from id
 	// Required: true
diff --git a/generated/models/channel_create_tx.go b/generated/models/channel_create_tx.go
index c30dd46a..62c6d69f 100644
--- a/generated/models/channel_create_tx.go
+++ b/generated/models/channel_create_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelCreateTx channel create tx
@@ -21,15 +21,15 @@ type ChannelCreateTx struct {
 
 	// channel reserve
 	// Required: true
-	ChannelReserve big.Int `json:"channel_reserve"`
+	ChannelReserve utils.BigInt `json:"channel_reserve"`
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// initiator amount
 	// Required: true
-	InitiatorAmount big.Int `json:"initiator_amount"`
+	InitiatorAmount utils.BigInt `json:"initiator_amount"`
 
 	// initiator id
 	// Required: true
@@ -46,11 +46,11 @@ type ChannelCreateTx struct {
 
 	// push amount
 	// Required: true
-	PushAmount big.Int `json:"push_amount"`
+	PushAmount utils.BigInt `json:"push_amount"`
 
 	// responder amount
 	// Required: true
-	ResponderAmount big.Int `json:"responder_amount"`
+	ResponderAmount utils.BigInt `json:"responder_amount"`
 
 	// responder id
 	// Required: true
diff --git a/generated/models/channel_deposit_tx.go b/generated/models/channel_deposit_tx.go
index affcb232..d2c30c29 100644
--- a/generated/models/channel_deposit_tx.go
+++ b/generated/models/channel_deposit_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelDepositTx channel deposit tx
@@ -21,7 +21,7 @@ type ChannelDepositTx struct {
 
 	// amount
 	// Required: true
-	Amount big.Int `json:"amount"`
+	Amount utils.BigInt `json:"amount"`
 
 	// channel id
 	// Required: true
@@ -29,7 +29,7 @@ type ChannelDepositTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// from id
 	// Required: true
diff --git a/generated/models/channel_force_progress_tx.go b/generated/models/channel_force_progress_tx.go
index d87e1ca5..15175eb0 100644
--- a/generated/models/channel_force_progress_tx.go
+++ b/generated/models/channel_force_progress_tx.go
@@ -17,7 +17,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelForceProgressTx channel force progress tx
@@ -30,7 +30,7 @@ type ChannelForceProgressTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// from id
 	// Required: true
@@ -78,7 +78,7 @@ func (m *ChannelForceProgressTx) UnmarshalJSON(raw []byte) error {
 	var data struct {
 		ChannelID EncodedHash `json:"channel_id"`
 
-		Fee big.Int `json:"fee"`
+		Fee utils.BigInt `json:"fee"`
 
 		FromID EncodedHash `json:"from_id"`
 
@@ -153,7 +153,7 @@ func (m ChannelForceProgressTx) MarshalJSON() ([]byte, error) {
 	b1, err = json.Marshal(struct {
 		ChannelID EncodedHash `json:"channel_id"`
 
-		Fee big.Int `json:"fee"`
+		Fee utils.BigInt `json:"fee"`
 
 		FromID EncodedHash `json:"from_id"`
 
diff --git a/generated/models/channel_settle_tx.go b/generated/models/channel_settle_tx.go
index 6e02fab0..10b35631 100644
--- a/generated/models/channel_settle_tx.go
+++ b/generated/models/channel_settle_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelSettleTx channel settle tx
@@ -25,7 +25,7 @@ type ChannelSettleTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// from id
 	// Required: true
@@ -33,7 +33,7 @@ type ChannelSettleTx struct {
 
 	// initiator amount final
 	// Required: true
-	InitiatorAmountFinal big.Int `json:"initiator_amount_final"`
+	InitiatorAmountFinal utils.BigInt `json:"initiator_amount_final"`
 
 	// nonce
 	// Required: true
@@ -42,7 +42,7 @@ type ChannelSettleTx struct {
 
 	// responder amount final
 	// Required: true
-	ResponderAmountFinal big.Int `json:"responder_amount_final"`
+	ResponderAmountFinal utils.BigInt `json:"responder_amount_final"`
 
 	// ttl
 	// Minimum: 0
diff --git a/generated/models/channel_sla_s_h_tx.go b/generated/models/channel_sla_s_h_tx.go
index e22fa503..3768c780 100644
--- a/generated/models/channel_sla_s_h_tx.go
+++ b/generated/models/channel_sla_s_h_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelSLASHTx channel slash tx
@@ -25,7 +25,7 @@ type ChannelSLASHTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// from id
 	// Required: true
diff --git a/generated/models/channel_snapshot_solo_tx.go b/generated/models/channel_snapshot_solo_tx.go
index 7ff36fe2..2dcc46fa 100644
--- a/generated/models/channel_snapshot_solo_tx.go
+++ b/generated/models/channel_snapshot_solo_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelSnapshotSoloTx channel snapshot solo tx
@@ -25,7 +25,7 @@ type ChannelSnapshotSoloTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// from id
 	// Required: true
diff --git a/generated/models/channel_withdraw_tx.go b/generated/models/channel_withdraw_tx.go
index 210ad97c..a2a3faba 100644
--- a/generated/models/channel_withdraw_tx.go
+++ b/generated/models/channel_withdraw_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ChannelWithdrawTx channel withdraw tx
@@ -21,7 +21,7 @@ type ChannelWithdrawTx struct {
 
 	// amount
 	// Required: true
-	Amount big.Int `json:"amount"`
+	Amount utils.BigInt `json:"amount"`
 
 	// channel id
 	// Required: true
@@ -29,7 +29,7 @@ type ChannelWithdrawTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// nonce
 	// Required: true
diff --git a/generated/models/contract_call_compute.go b/generated/models/contract_call_compute.go
index e4083128..d2af0a0d 100644
--- a/generated/models/contract_call_compute.go
+++ b/generated/models/contract_call_compute.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ContractCallCompute contract call compute
@@ -40,7 +40,7 @@ type ContractCallCompute struct {
 
 	// Transaction fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// Contract call data function (deprecated, use call)
 	Function string `json:"function,omitempty"`
diff --git a/generated/models/contract_call_tx.go b/generated/models/contract_call_tx.go
index 1d2393ef..ea8d35d4 100644
--- a/generated/models/contract_call_tx.go
+++ b/generated/models/contract_call_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ContractCallTx contract call tx
@@ -38,7 +38,7 @@ type ContractCallTx struct {
 
 	// Transaction fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// Contract gas
 	// Required: true
diff --git a/generated/models/contract_create_compute.go b/generated/models/contract_create_compute.go
index 4e6b9db5..ef68d1ac 100644
--- a/generated/models/contract_create_compute.go
+++ b/generated/models/contract_create_compute.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ContractCreateCompute contract create compute
@@ -41,7 +41,7 @@ type ContractCreateCompute struct {
 
 	// Transaction fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// Contract gas
 	// Required: true
diff --git a/generated/models/contract_create_tx.go b/generated/models/contract_create_tx.go
index 0c859006..84a82b9c 100644
--- a/generated/models/contract_create_tx.go
+++ b/generated/models/contract_create_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // ContractCreateTx contract create tx
@@ -39,7 +39,7 @@ type ContractCreateTx struct {
 
 	// Transaction fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// Contract gas
 	// Required: true
diff --git a/generated/models/name_claim_tx.go b/generated/models/name_claim_tx.go
index b1aef121..86ad8e1d 100644
--- a/generated/models/name_claim_tx.go
+++ b/generated/models/name_claim_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // NameClaimTx name claim tx
@@ -25,7 +25,7 @@ type NameClaimTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// name
 	// Required: true
diff --git a/generated/models/name_preclaim_tx.go b/generated/models/name_preclaim_tx.go
index fe3e4483..fa217546 100644
--- a/generated/models/name_preclaim_tx.go
+++ b/generated/models/name_preclaim_tx.go
@@ -11,7 +11,7 @@ import (
 	"github.com/go-openapi/errors"
 	"github.com/go-openapi/swag"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // NamePreclaimTx name preclaim tx
@@ -28,7 +28,7 @@ type NamePreclaimTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// nonce
 	Nonce uint64 `json:"nonce,omitempty"`
diff --git a/generated/models/name_revoke_tx.go b/generated/models/name_revoke_tx.go
index 41ba4e3b..62b56862 100644
--- a/generated/models/name_revoke_tx.go
+++ b/generated/models/name_revoke_tx.go
@@ -11,7 +11,7 @@ import (
 	"github.com/go-openapi/errors"
 	"github.com/go-openapi/swag"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // NameRevokeTx name revoke tx
@@ -24,7 +24,7 @@ type NameRevokeTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// name id
 	// Required: true
diff --git a/generated/models/name_transfer_tx.go b/generated/models/name_transfer_tx.go
index 91beffbf..d4b6ac23 100644
--- a/generated/models/name_transfer_tx.go
+++ b/generated/models/name_transfer_tx.go
@@ -11,7 +11,7 @@ import (
 	"github.com/go-openapi/errors"
 	"github.com/go-openapi/swag"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // NameTransferTx name transfer tx
@@ -24,7 +24,7 @@ type NameTransferTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// name id
 	// Required: true
diff --git a/generated/models/name_update_tx.go b/generated/models/name_update_tx.go
index b1b97f07..4f5a018b 100644
--- a/generated/models/name_update_tx.go
+++ b/generated/models/name_update_tx.go
@@ -14,7 +14,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // NameUpdateTx name update tx
@@ -31,7 +31,7 @@ type NameUpdateTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// name id
 	// Required: true
diff --git a/generated/models/oracle_extend_tx.go b/generated/models/oracle_extend_tx.go
index a60f0be2..6302c3fa 100644
--- a/generated/models/oracle_extend_tx.go
+++ b/generated/models/oracle_extend_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // OracleExtendTx oracle extend tx
@@ -21,7 +21,7 @@ type OracleExtendTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// nonce
 	Nonce uint64 `json:"nonce,omitempty"`
diff --git a/generated/models/oracle_query.go b/generated/models/oracle_query.go
index 860adedb..569d4d71 100644
--- a/generated/models/oracle_query.go
+++ b/generated/models/oracle_query.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // OracleQuery oracle query
@@ -21,7 +21,7 @@ type OracleQuery struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// id
 	// Required: true
diff --git a/generated/models/oracle_query_tx.go b/generated/models/oracle_query_tx.go
index 77012c57..91b74e41 100644
--- a/generated/models/oracle_query_tx.go
+++ b/generated/models/oracle_query_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // OracleQueryTx oracle query tx
@@ -21,7 +21,7 @@ type OracleQueryTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// Sender nonce
 	Nonce uint64 `json:"nonce,omitempty"`
@@ -36,7 +36,7 @@ type OracleQueryTx struct {
 
 	// query fee
 	// Required: true
-	QueryFee big.Int `json:"query_fee"`
+	QueryFee utils.BigInt `json:"query_fee"`
 
 	// query ttl
 	// Required: true
diff --git a/generated/models/oracle_register_tx.go b/generated/models/oracle_register_tx.go
index 09450ce4..c636bf64 100644
--- a/generated/models/oracle_register_tx.go
+++ b/generated/models/oracle_register_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // OracleRegisterTx oracle register tx
@@ -25,7 +25,7 @@ type OracleRegisterTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// nonce
 	Nonce uint64 `json:"nonce,omitempty"`
@@ -36,7 +36,7 @@ type OracleRegisterTx struct {
 
 	// query fee
 	// Required: true
-	QueryFee big.Int `json:"query_fee"`
+	QueryFee utils.BigInt `json:"query_fee"`
 
 	// query format
 	// Required: true
diff --git a/generated/models/oracle_respond_tx.go b/generated/models/oracle_respond_tx.go
index a302e2dc..f37b7eab 100644
--- a/generated/models/oracle_respond_tx.go
+++ b/generated/models/oracle_respond_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // OracleRespondTx oracle respond tx
@@ -21,7 +21,7 @@ type OracleRespondTx struct {
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// Oracle nonce
 	Nonce uint64 `json:"nonce,omitempty"`
diff --git a/generated/models/registered_oracle.go b/generated/models/registered_oracle.go
index 3c24aa75..4d5be5f7 100644
--- a/generated/models/registered_oracle.go
+++ b/generated/models/registered_oracle.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // RegisteredOracle registered oracle
@@ -25,7 +25,7 @@ type RegisteredOracle struct {
 
 	// query fee
 	// Required: true
-	QueryFee big.Int `json:"query_fee"`
+	QueryFee utils.BigInt `json:"query_fee"`
 
 	// query format
 	// Required: true
diff --git a/generated/models/spend_tx.go b/generated/models/spend_tx.go
index 4a9b8159..6b494a86 100644
--- a/generated/models/spend_tx.go
+++ b/generated/models/spend_tx.go
@@ -12,7 +12,7 @@ import (
 	"github.com/go-openapi/swag"
 	"github.com/go-openapi/validate"
 
-	big "math/big"
+	utils "github.com/aeternity/aepp-sdk-go/utils"
 )
 
 // SpendTx spend tx
@@ -21,11 +21,11 @@ type SpendTx struct {
 
 	// amount
 	// Required: true
-	Amount big.Int `json:"amount"`
+	Amount utils.BigInt `json:"amount"`
 
 	// fee
 	// Required: true
-	Fee big.Int `json:"fee"`
+	Fee utils.BigInt `json:"fee"`
 
 	// nonce
 	Nonce uint64 `json:"nonce,omitempty"`
diff --git a/utils/utils.go b/utils/utils.go
index a8e81ed9..656aa399 100644
--- a/utils/utils.go
+++ b/utils/utils.go
@@ -2,12 +2,15 @@ package utils
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
+	"math/big"
 	"os"
 	"strconv"
 	"strings"
 	"syscall"
 
+	"github.com/go-openapi/strfmt"
 	gonanoid "github.com/matoous/go-nanoid"
 	"golang.org/x/crypto/ssh/terminal"
 )
@@ -131,3 +134,17 @@ func AskPassword(question string) (password string, err error) {
 	password = string(bytePassword)
 	return
 }
+
+// BigInt is used by swagger as a big.Int type with Validate() function
+type BigInt big.Int
+
+// Validate only checks that the number is >=0
+func (b *BigInt) Validate(formats strfmt.Registry) error {
+	var zero big.Int
+	var convertedCustomBigInt = big.Int(*b)
+
+	if convertedCustomBigInt.Cmp(&zero) != 1 {
+		return errors.New("swagger deserialization: Balance Validation failed")
+	}
+	return nil
+}