diff --git a/internal/ethapi/api.go b/internal/ethapi/api.go
index da779a9eee..feb7b99fc2 100644
--- a/internal/ethapi/api.go
+++ b/internal/ethapi/api.go
@@ -448,14 +448,15 @@ func (s *PrivateAccountAPI) SignTransaction(ctx context.Context, args Transactio
 	if args.Gas == nil {
 		return nil, fmt.Errorf("gas not specified")
 	}
-	if args.GasPrice == nil {
-		return nil, fmt.Errorf("gasPrice not specified")
+	if args.GasPrice == nil && (args.MaxFeePerGas == nil || args.MaxPriorityFeePerGas == nil) {
+		return nil, fmt.Errorf("missing gasPrice or maxFeePerGas/maxPriorityFeePerGas")
 	}
 	if args.Nonce == nil {
 		return nil, fmt.Errorf("nonce not specified")
 	}
 	// Before actually sign the transaction, ensure the transaction fee is reasonable.
-	if err := checkTxFee(args.GasPrice.ToInt(), uint64(*args.Gas), s.b.RPCTxFeeCap()); err != nil {
+	tx := args.toTransaction()
+	if err := checkTxFee(tx.GasPrice(), tx.Gas(), s.b.RPCTxFeeCap()); err != nil {
 		return nil, err
 	}
 	signed, err := s.signTransaction(ctx, &args, passwd)
@@ -1697,8 +1698,9 @@ func (s *PublicTransactionPoolAPI) SendTransaction(ctx context.Context, args Tra
 	return SubmitTransaction(ctx, s.b, signed)
 }
 
-// FillTransaction fills the defaults (nonce, gas, gasPrice) on a given unsigned transaction,
-// and returns it to the caller for further processing (signing + broadcast)
+// FillTransaction fills the defaults (nonce, gas, gasPrice or 1559 fields)
+// on a given unsigned transaction, and returns it to the caller for further
+// processing (signing + broadcast).
 func (s *PublicTransactionPoolAPI) FillTransaction(ctx context.Context, args TransactionArgs) (*SignTransactionResult, error) {
 	// Set some sanity defaults and terminate on failure
 	if err := args.setDefaults(ctx, s.b); err != nil {
@@ -1761,8 +1763,8 @@ func (s *PublicTransactionPoolAPI) SignTransaction(ctx context.Context, args Tra
 	if args.Gas == nil {
 		return nil, fmt.Errorf("gas not specified")
 	}
-	if args.GasPrice == nil {
-		return nil, fmt.Errorf("gasPrice not specified")
+	if args.GasPrice == nil && (args.MaxPriorityFeePerGas == nil || args.MaxFeePerGas == nil) {
+		return nil, fmt.Errorf("missing gasPrice or maxFeePerGas/maxPriorityFeePerGas")
 	}
 	if args.Nonce == nil {
 		return nil, fmt.Errorf("nonce not specified")
@@ -1771,18 +1773,19 @@ func (s *PublicTransactionPoolAPI) SignTransaction(ctx context.Context, args Tra
 		return nil, err
 	}
 	// Before actually sign the transaction, ensure the transaction fee is reasonable.
-	if err := checkTxFee(args.GasPrice.ToInt(), uint64(*args.Gas), s.b.RPCTxFeeCap()); err != nil {
+	tx := args.toTransaction()
+	if err := checkTxFee(tx.GasPrice(), tx.Gas(), s.b.RPCTxFeeCap()); err != nil {
 		return nil, err
 	}
-	tx, err := s.sign(args.from(), args.toTransaction())
+	signed, err := s.sign(args.from(), tx)
 	if err != nil {
 		return nil, err
 	}
-	data, err := tx.MarshalBinary()
+	data, err := signed.MarshalBinary()
 	if err != nil {
 		return nil, err
 	}
-	return &SignTransactionResult{data, tx}, nil
+	return &SignTransactionResult{data, signed}, nil
 }
 
 // PendingTransactions returns the transactions that are in the transaction pool
diff --git a/internal/ethapi/transaction_args.go b/internal/ethapi/transaction_args.go
index 220eb22b70..1fbaaeacbf 100644
--- a/internal/ethapi/transaction_args.go
+++ b/internal/ethapi/transaction_args.go
@@ -49,7 +49,7 @@ type TransactionArgs struct {
 	Data  *hexutil.Bytes `json:"data"`
 	Input *hexutil.Bytes `json:"input"`
 
-	// For non-legacy transactions
+	// Introduced by AccessListTxType transaction.
 	AccessList *types.AccessList `json:"accessList,omitempty"`
 	ChainID    *hexutil.Big      `json:"chainId,omitempty"`
 }
@@ -108,6 +108,9 @@ func (args *TransactionArgs) setDefaults(ctx context.Context, b Backend) error {
 				return err
 			}
 			if b.ChainConfig().IsLondon(head.Number) {
+				// The legacy tx gas price suggestion should not add 2x base fee
+				// because all fees are consumed, so it would result in a spiral
+				// upwards.
 				price.Add(price, head.BaseFee)
 			}
 			args.GasPrice = (*hexutil.Big)(price)