diff --git a/common/math/big.go b/common/math/big.go
index 704ca40a93..0b67a1b503 100644
--- a/common/math/big.go
+++ b/common/math/big.go
@@ -18,6 +18,7 @@
 package math
 
 import (
+	"fmt"
 	"math/big"
 )
 
@@ -35,6 +36,24 @@ const (
 	wordBytes = wordBits / 8
 )
 
+// HexOrDecimal256 marshals big.Int as hex or decimal.
+type HexOrDecimal256 big.Int
+
+// UnmarshalText implements encoding.TextUnmarshaler.
+func (i *HexOrDecimal256) UnmarshalText(input []byte) error {
+	bigint, ok := ParseBig256(string(input))
+	if !ok {
+		return fmt.Errorf("invalid hex or decimal integer %q", input)
+	}
+	*i = HexOrDecimal256(*bigint)
+	return nil
+}
+
+// MarshalText implements encoding.TextMarshaler.
+func (i *HexOrDecimal256) MarshalText() ([]byte, error) {
+	return []byte(fmt.Sprintf("%#x", (*big.Int)(i))), nil
+}
+
 // ParseBig256 parses s as a 256 bit integer in decimal or hexadecimal syntax.
 // Leading zeros are accepted. The empty string parses as zero.
 func ParseBig256(s string) (*big.Int, bool) {
diff --git a/common/math/big_test.go b/common/math/big_test.go
index 6eb13f4f12..deff254658 100644
--- a/common/math/big_test.go
+++ b/common/math/big_test.go
@@ -23,7 +23,7 @@ import (
 	"testing"
 )
 
-func TestParseBig256(t *testing.T) {
+func TestHexOrDecimal256(t *testing.T) {
 	tests := []struct {
 		input string
 		num   *big.Int
@@ -47,13 +47,14 @@ func TestParseBig256(t *testing.T) {
 		{"115792089237316195423570985008687907853269984665640564039457584007913129639936", nil, false},
 	}
 	for _, test := range tests {
-		num, ok := ParseBig256(test.input)
-		if ok != test.ok {
-			t.Errorf("ParseBig(%q) -> ok = %t, want %t", test.input, ok, test.ok)
+		var num HexOrDecimal256
+		err := num.UnmarshalText([]byte(test.input))
+		if (err == nil) != test.ok {
+			t.Errorf("ParseBig(%q) -> (err == nil) == %t, want %t", test.input, err == nil, test.ok)
 			continue
 		}
-		if num != nil && test.num != nil && num.Cmp(test.num) != 0 {
-			t.Errorf("ParseBig(%q) -> %d, want %d", test.input, num, test.num)
+		if test.num != nil && (*big.Int)(&num).Cmp(test.num) != 0 {
+			t.Errorf("ParseBig(%q) -> %d, want %d", test.input, (*big.Int)(&num), test.num)
 		}
 	}
 }
diff --git a/common/math/integer.go b/common/math/integer.go
index a3eeee27e7..7eff4d3b00 100644
--- a/common/math/integer.go
+++ b/common/math/integer.go
@@ -16,7 +16,10 @@
 
 package math
 
-import "strconv"
+import (
+	"fmt"
+	"strconv"
+)
 
 const (
 	// Integer limit values.
@@ -34,6 +37,24 @@ const (
 	MaxUint64 = 1<<64 - 1
 )
 
+// HexOrDecimal64 marshals uint64 as hex or decimal.
+type HexOrDecimal64 uint64
+
+// UnmarshalText implements encoding.TextUnmarshaler.
+func (i *HexOrDecimal64) UnmarshalText(input []byte) error {
+	int, ok := ParseUint64(string(input))
+	if !ok {
+		return fmt.Errorf("invalid hex or decimal integer %q", input)
+	}
+	*i = HexOrDecimal64(int)
+	return nil
+}
+
+// MarshalText implements encoding.TextMarshaler.
+func (i HexOrDecimal64) MarshalText() ([]byte, error) {
+	return []byte(fmt.Sprintf("%#x", uint64(i))), nil
+}
+
 // ParseUint64 parses s as an integer in decimal or hexadecimal syntax.
 // Leading zeros are accepted. The empty string parses as zero.
 func ParseUint64(s string) (uint64, bool) {
diff --git a/common/math/integer_test.go b/common/math/integer_test.go
index 05bba221f9..b31c7c26c2 100644
--- a/common/math/integer_test.go
+++ b/common/math/integer_test.go
@@ -65,7 +65,7 @@ func TestOverflow(t *testing.T) {
 	}
 }
 
-func TestParseUint64(t *testing.T) {
+func TestHexOrDecimal64(t *testing.T) {
 	tests := []struct {
 		input string
 		num   uint64
@@ -88,12 +88,13 @@ func TestParseUint64(t *testing.T) {
 		{"18446744073709551617", 0, false},
 	}
 	for _, test := range tests {
-		num, ok := ParseUint64(test.input)
-		if ok != test.ok {
-			t.Errorf("ParseUint64(%q) -> ok = %t, want %t", test.input, ok, test.ok)
+		var num HexOrDecimal64
+		err := num.UnmarshalText([]byte(test.input))
+		if (err == nil) != test.ok {
+			t.Errorf("ParseUint64(%q) -> (err == nil) = %t, want %t", test.input, err == nil, test.ok)
 			continue
 		}
-		if ok && num != test.num {
+		if err == nil && uint64(num) != test.num {
 			t.Errorf("ParseUint64(%q) -> %d, want %d", test.input, num, test.num)
 		}
 	}