diff --git a/common/fee_test.go b/common/fee_test.go
index 63219e8..0b6be7f 100644
--- a/common/fee_test.go
+++ b/common/fee_test.go
@@ -48,8 +48,11 @@ func TestCalcFeeAmount(t *testing.T) {
 }
 
 func TestFeePrintSQLSwitch(t *testing.T) {
+	debug := false
 	for i := 0; i < 256; i++ {
 		f := FeeSelector(i).Percentage()
-		fmt.Printf("        WHEN $1 = %03d THEN %.6e\n", i, f)
+		if debug {
+			fmt.Printf("        WHEN $1 = %03d THEN %.6e\n", i, f)
+		}
 	}
 }
diff --git a/common/l1tx.go b/common/l1tx.go
index ceddb31..a98ecdf 100644
--- a/common/l1tx.go
+++ b/common/l1tx.go
@@ -146,8 +146,11 @@ func (tx L1Tx) Tx() Tx {
 	return genericTx
 }
 
-// BytesUser encodes a L1Tx into []byte
-func (tx *L1Tx) BytesUser() ([]byte, error) {
+// BytesGeneric returns the generic representation of a L1Tx. This method is
+// used to compute the []byte representation of a L1UserTx, and also to compute
+// the L1TxData for the ZKInputs (at the HashGlobalInputs), using this method
+// for L1CoordinatorTxs & L1UserTxs (for the ZKInputs case).
+func (tx *L1Tx) BytesGeneric() ([]byte, error) {
 	var b [L1UserTxBytesLen]byte
 	copy(b[0:20], tx.FromEthAddr.Bytes())
 	pkCompL := tx.FromBJJ.Compress()
@@ -177,8 +180,19 @@ func (tx *L1Tx) BytesUser() ([]byte, error) {
 	return b[:], nil
 }
 
+// BytesUser encodes a L1UserTx into []byte
+func (tx *L1Tx) BytesUser() ([]byte, error) {
+	if !tx.UserOrigin {
+		return nil, fmt.Errorf("Can not calculate BytesUser() for a L1CoordinatorTx")
+	}
+	return tx.BytesGeneric()
+}
+
 // BytesCoordinatorTx encodes a L1CoordinatorTx into []byte
 func (tx *L1Tx) BytesCoordinatorTx(compressedSignatureBytes []byte) ([]byte, error) {
+	if tx.UserOrigin {
+		return nil, fmt.Errorf("Can not calculate BytesCoordinatorTx() for a L1UserTx")
+	}
 	var b [L1CoordinatorTxBytesLen]byte
 	v := compressedSignatureBytes[64]
 	s := compressedSignatureBytes[32:64]
@@ -210,7 +224,6 @@ func L1UserTxFromBytes(b []byte) (*L1Tx, error) {
 	var pkComp babyjub.PublicKeyComp
 	copy(pkComp[:], pkCompL)
 	tx.FromBJJ, err = pkComp.Decompress()
-
 	if err != nil {
 		return nil, err
 	}
diff --git a/common/l1tx_test.go b/common/l1tx_test.go
index c04b08a..9b952d0 100644
--- a/common/l1tx_test.go
+++ b/common/l1tx_test.go
@@ -109,6 +109,7 @@ func TestL1TxByteParsersCompatibility(t *testing.T) {
 		FromIdx:     Idx(29767899),
 		FromBJJ:     pk,
 		FromEthAddr: ethCommon.HexToAddress("0x85dab5b9e2e361d0c208d77be90efcc0439b0a53"),
+		UserOrigin:  true,
 	}
 
 	expected, err := utils.HexDecode("85dab5b9e2e361d0c208d77be90efcc0439b0a530dd02deb2c81068e7a0f7e327df80b4ab79ee1f41a7def613e73a20c32eece5a000001c638db8be880f00020039c0000053cb88d")
diff --git a/common/l2tx.go b/common/l2tx.go
index a2bb296..2ce279c 100644
--- a/common/l2tx.go
+++ b/common/l2tx.go
@@ -105,49 +105,54 @@ func L2TxsToPoolL2Txs(txs []L2Tx) []PoolL2Tx {
 
 // Bytes encodes a L2Tx into []byte
 func (tx *L2Tx) Bytes(nLevels int) ([]byte, error) {
-	fromIdxNumBytes := nLevels / 8 //nolint:gomnd
-	toIdxNumBytes := nLevels / 8   //nolint:gomnd
-	var b []byte
+	idxLen := nLevels / 8 //nolint:gomnd
+
+	b := make([]byte, ((nLevels*2)+16+8)/8)
+
 	fromIdxBytes, err := tx.FromIdx.Bytes()
 	if err != nil {
 		return nil, err
 	}
-	b = append(b, fromIdxBytes[6-fromIdxNumBytes:]...)
+	copy(b[0:idxLen], fromIdxBytes[6-idxLen:]) // [6-idxLen:] as is BigEndian
+
 	toIdxBytes, err := tx.ToIdx.Bytes()
 	if err != nil {
 		return nil, err
 	}
-	b = append(b, toIdxBytes[6-toIdxNumBytes:]...)
+	copy(b[idxLen:idxLen*2], toIdxBytes[6-idxLen:])
+
 	amountFloat16, err := NewFloat16(tx.Amount)
 	if err != nil {
 		return nil, err
 	}
-	b = append(b, amountFloat16.Bytes()...)
-	b = append(b, byte(tx.Fee))
+
+	copy(b[idxLen*2:idxLen*2+2], amountFloat16.Bytes())
+	b[idxLen*2+2] = byte(tx.Fee)
+
 	return b[:], nil
 }
 
 // L2TxFromBytes decodes a L1Tx from []byte
 func L2TxFromBytes(b []byte, nLevels int) (*L2Tx, error) {
-	fromIdxNumByte := nLevels / 8              //nolint:gomnd
-	toIdxNumByte := fromIdxNumByte + nLevels/8 //nolint:gomnd
-	amountLenBytes := 2
-	amountNumByte := toIdxNumByte + amountLenBytes
+	idxLen := nLevels / 8 //nolint:gomnd
 	tx := &L2Tx{}
 	var err error
+
 	var paddedFromIdxBytes [6]byte
-	copy(paddedFromIdxBytes[6-len(b[0:fromIdxNumByte]):], b[0:fromIdxNumByte])
+	copy(paddedFromIdxBytes[6-idxLen:], b[0:idxLen])
 	tx.FromIdx, err = IdxFromBytes(paddedFromIdxBytes[:])
 	if err != nil {
 		return nil, err
 	}
+
 	var paddedToIdxBytes [6]byte
-	copy(paddedToIdxBytes[6-len(b[fromIdxNumByte:toIdxNumByte]):6], b[fromIdxNumByte:toIdxNumByte])
+	copy(paddedToIdxBytes[6-idxLen:6], b[idxLen:idxLen*2])
 	tx.ToIdx, err = IdxFromBytes(paddedToIdxBytes[:])
 	if err != nil {
 		return nil, err
 	}
-	tx.Amount = Float16FromBytes(b[toIdxNumByte:amountNumByte]).BigInt()
-	tx.Fee = FeeSelector(b[amountNumByte])
+
+	tx.Amount = Float16FromBytes(b[idxLen*2 : idxLen*2+2]).BigInt()
+	tx.Fee = FeeSelector(b[idxLen*2+2])
 	return tx, nil
 }