diff --git a/common/math/big.go b/common/math/big.go
index 78e3c8255d..203642565c 100644
--- a/common/math/big.go
+++ b/common/math/big.go
@@ -71,7 +71,7 @@ func (i *HexOrDecimal256) MarshalText() ([]byte, error) {
 	if i == nil {
 		return []byte("0x0"), nil
 	}
-	return []byte(fmt.Sprintf("%#x", (*big.Int)(i))), nil
+	return fmt.Appendf(nil, "%#x", (*big.Int)(i)), nil
 }
 
 // ParseBig256 parses s as a 256 bit integer in decimal or hexadecimal syntax.
diff --git a/common/math/integer.go b/common/math/integer.go
index 25ced87053..dfcb0aecc4 100644
--- a/common/math/integer.go
+++ b/common/math/integer.go
@@ -48,7 +48,7 @@ func (i *HexOrDecimal64) UnmarshalText(input []byte) error {
 
 // MarshalText implements encoding.TextMarshaler.
 func (i HexOrDecimal64) MarshalText() ([]byte, error) {
-	return []byte(fmt.Sprintf("%#x", uint64(i))), nil
+	return fmt.Appendf(nil, "%#x", uint64(i)), nil
 }
 
 // ParseUint64 parses s as an integer in decimal or hexadecimal syntax.
diff --git a/contracts/utils.go b/contracts/utils.go
index 2d65fe2217..75c37e59e5 100644
--- a/contracts/utils.go
+++ b/contracts/utils.go
@@ -279,7 +279,7 @@ func BuildValidatorFromM2(listM2 []int64) []byte {
 	var validatorBytes []byte
 	for _, numberM2 := range listM2 {
 		// Convert number to byte.
-		m2Byte := common.LeftPadBytes([]byte(fmt.Sprintf("%d", numberM2)), utils.M2ByteLength)
+		m2Byte := common.LeftPadBytes(fmt.Appendf(nil, "%d", numberM2), utils.M2ByteLength)
 		validatorBytes = append(validatorBytes, m2Byte...)
 	}