diff --git a/src/math/big/int.go b/src/math/big/int.go
index 84485a2..ac5c1f0 100644
--- a/src/math/big/int.go
+++ b/src/math/big/int.go
@@ -929,65 +929,3 @@
 	z.neg = true // z cannot be zero if x is positive
 	return z
 }
-
-// Gob codec version. Permits backward-compatible changes to the encoding.
-const intGobVersion byte = 1
-
-// GobEncode implements the gob.GobEncoder interface.
-func (x *Int) GobEncode() ([]byte, error) {
-	if x == nil {
-		return nil, nil
-	}
-	buf := make([]byte, 1+len(x.abs)*_S) // extra byte for version and sign bit
-	i := x.abs.bytes(buf) - 1            // i >= 0
-	b := intGobVersion << 1              // make space for sign bit
-	if x.neg {
-		b |= 1
-	}
-	buf[i] = b
-	return buf[i:], nil
-}
-
-// GobDecode implements the gob.GobDecoder interface.
-func (z *Int) GobDecode(buf []byte) error {
-	if len(buf) == 0 {
-		// Other side sent a nil or default value.
-		*z = Int{}
-		return nil
-	}
-	b := buf[0]
-	if b>>1 != intGobVersion {
-		return fmt.Errorf("Int.GobDecode: encoding version %d not supported", b>>1)
-	}
-	z.neg = b&1 != 0
-	z.abs = z.abs.setBytes(buf[1:])
-	return nil
-}
-
-// MarshalJSON implements the json.Marshaler interface.
-func (z *Int) MarshalJSON() ([]byte, error) {
-	// TODO(gri): get rid of the []byte/string conversions
-	return []byte(z.String()), nil
-}
-
-// UnmarshalJSON implements the json.Unmarshaler interface.
-func (z *Int) UnmarshalJSON(text []byte) error {
-	// TODO(gri): get rid of the []byte/string conversions
-	if _, ok := z.SetString(string(text), 0); !ok {
-		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Int", text)
-	}
-	return nil
-}
-
-// MarshalText implements the encoding.TextMarshaler interface.
-func (z *Int) MarshalText() (text []byte, err error) {
-	return []byte(z.String()), nil
-}
-
-// UnmarshalText implements the encoding.TextUnmarshaler interface.
-func (z *Int) UnmarshalText(text []byte) error {
-	if _, ok := z.SetString(string(text), 0); !ok {
-		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Int", text)
-	}
-	return nil
-}
diff --git a/src/math/big/int_test.go b/src/math/big/int_test.go
index 5b80509..72c2c98 100644
--- a/src/math/big/int_test.go
+++ b/src/math/big/int_test.go
@@ -6,10 +6,7 @@
 
 import (
 	"bytes"
-	"encoding/gob"
 	"encoding/hex"
-	"encoding/json"
-	"encoding/xml"
 	"fmt"
 	"math/rand"
 	"testing"
@@ -1453,138 +1450,6 @@
 	panic(failureMsg)
 }
 
-var encodingTests = []string{
-	"-539345864568634858364538753846587364875430589374589",
-	"-678645873",
-	"-100",
-	"-2",
-	"-1",
-	"0",
-	"1",
-	"2",
-	"10",
-	"42",
-	"1234567890",
-	"298472983472983471903246121093472394872319615612417471234712061",
-}
-
-func TestIntGobEncoding(t *testing.T) {
-	var medium bytes.Buffer
-	enc := gob.NewEncoder(&medium)
-	dec := gob.NewDecoder(&medium)
-	for _, test := range encodingTests {
-		medium.Reset() // empty buffer for each test case (in case of failures)
-		var tx Int
-		tx.SetString(test, 10)
-		if err := enc.Encode(&tx); err != nil {
-			t.Errorf("encoding of %s failed: %s", &tx, err)
-		}
-		var rx Int
-		if err := dec.Decode(&rx); err != nil {
-			t.Errorf("decoding of %s failed: %s", &tx, err)
-		}
-		if rx.Cmp(&tx) != 0 {
-			t.Errorf("transmission of %s failed: got %s want %s", &tx, &rx, &tx)
-		}
-	}
-}
-
-// Sending a nil Int pointer (inside a slice) on a round trip through gob should yield a zero.
-// TODO: top-level nils.
-func TestGobEncodingNilIntInSlice(t *testing.T) {
-	buf := new(bytes.Buffer)
-	enc := gob.NewEncoder(buf)
-	dec := gob.NewDecoder(buf)
-
-	var in = make([]*Int, 1)
-	err := enc.Encode(&in)
-	if err != nil {
-		t.Errorf("gob encode failed: %q", err)
-	}
-	var out []*Int
-	err = dec.Decode(&out)
-	if err != nil {
-		t.Fatalf("gob decode failed: %q", err)
-	}
-	if len(out) != 1 {
-		t.Fatalf("wrong len; want 1 got %d", len(out))
-	}
-	var zero Int
-	if out[0].Cmp(&zero) != 0 {
-		t.Errorf("transmission of (*Int)(nill) failed: got %s want 0", out)
-	}
-}
-
-func TestIntJSONEncoding(t *testing.T) {
-	for _, test := range encodingTests {
-		var tx Int
-		tx.SetString(test, 10)
-		b, err := json.Marshal(&tx)
-		if err != nil {
-			t.Errorf("marshaling of %s failed: %s", &tx, err)
-		}
-		var rx Int
-		if err := json.Unmarshal(b, &rx); err != nil {
-			t.Errorf("unmarshaling of %s failed: %s", &tx, err)
-		}
-		if rx.Cmp(&tx) != 0 {
-			t.Errorf("JSON encoding of %s failed: got %s want %s", &tx, &rx, &tx)
-		}
-	}
-}
-
-var intVals = []string{
-	"-141592653589793238462643383279502884197169399375105820974944592307816406286",
-	"-1415926535897932384626433832795028841971",
-	"-141592653589793",
-	"-1",
-	"0",
-	"1",
-	"141592653589793",
-	"1415926535897932384626433832795028841971",
-	"141592653589793238462643383279502884197169399375105820974944592307816406286",
-}
-
-func TestIntJSONEncodingTextMarshaller(t *testing.T) {
-	for _, num := range intVals {
-		var tx Int
-		tx.SetString(num, 0)
-		b, err := json.Marshal(&tx)
-		if err != nil {
-			t.Errorf("marshaling of %s failed: %s", &tx, err)
-			continue
-		}
-		var rx Int
-		if err := json.Unmarshal(b, &rx); err != nil {
-			t.Errorf("unmarshaling of %s failed: %s", &tx, err)
-			continue
-		}
-		if rx.Cmp(&tx) != 0 {
-			t.Errorf("JSON encoding of %s failed: got %s want %s", &tx, &rx, &tx)
-		}
-	}
-}
-
-func TestIntXMLEncodingTextMarshaller(t *testing.T) {
-	for _, num := range intVals {
-		var tx Int
-		tx.SetString(num, 0)
-		b, err := xml.Marshal(&tx)
-		if err != nil {
-			t.Errorf("marshaling of %s failed: %s", &tx, err)
-			continue
-		}
-		var rx Int
-		if err := xml.Unmarshal(b, &rx); err != nil {
-			t.Errorf("unmarshaling of %s failed: %s", &tx, err)
-			continue
-		}
-		if rx.Cmp(&tx) != 0 {
-			t.Errorf("XML encoding of %s failed: got %s want %s", &tx, &rx, &tx)
-		}
-	}
-}
-
 func TestIssue2607(t *testing.T) {
 	// This code sequence used to hang.
 	n := NewInt(10)
diff --git a/src/math/big/intmarsh.go b/src/math/big/intmarsh.go
new file mode 100644
index 0000000..3c1efec
--- /dev/null
+++ b/src/math/big/intmarsh.go
@@ -0,0 +1,71 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements encoding/decoding of Ints.
+
+package big
+
+import "fmt"
+
+// Gob codec version. Permits backward-compatible changes to the encoding.
+const intGobVersion byte = 1
+
+// GobEncode implements the gob.GobEncoder interface.
+func (x *Int) GobEncode() ([]byte, error) {
+	if x == nil {
+		return nil, nil
+	}
+	buf := make([]byte, 1+len(x.abs)*_S) // extra byte for version and sign bit
+	i := x.abs.bytes(buf) - 1            // i >= 0
+	b := intGobVersion << 1              // make space for sign bit
+	if x.neg {
+		b |= 1
+	}
+	buf[i] = b
+	return buf[i:], nil
+}
+
+// GobDecode implements the gob.GobDecoder interface.
+func (z *Int) GobDecode(buf []byte) error {
+	if len(buf) == 0 {
+		// Other side sent a nil or default value.
+		*z = Int{}
+		return nil
+	}
+	b := buf[0]
+	if b>>1 != intGobVersion {
+		return fmt.Errorf("Int.GobDecode: encoding version %d not supported", b>>1)
+	}
+	z.neg = b&1 != 0
+	z.abs = z.abs.setBytes(buf[1:])
+	return nil
+}
+
+// MarshalJSON implements the json.Marshaler interface.
+func (z *Int) MarshalJSON() ([]byte, error) {
+	// TODO(gri): get rid of the []byte/string conversions
+	return []byte(z.String()), nil
+}
+
+// UnmarshalJSON implements the json.Unmarshaler interface.
+func (z *Int) UnmarshalJSON(text []byte) error {
+	// TODO(gri): get rid of the []byte/string conversions
+	if _, ok := z.SetString(string(text), 0); !ok {
+		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Int", text)
+	}
+	return nil
+}
+
+// MarshalText implements the encoding.TextMarshaler interface.
+func (z *Int) MarshalText() (text []byte, err error) {
+	return []byte(z.String()), nil
+}
+
+// UnmarshalText implements the encoding.TextUnmarshaler interface.
+func (z *Int) UnmarshalText(text []byte) error {
+	if _, ok := z.SetString(string(text), 0); !ok {
+		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Int", text)
+	}
+	return nil
+}
diff --git a/src/math/big/intmarsh_test.go b/src/math/big/intmarsh_test.go
new file mode 100644
index 0000000..c992f1c
--- /dev/null
+++ b/src/math/big/intmarsh_test.go
@@ -0,0 +1,145 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package big
+
+import (
+	"bytes"
+	"encoding/gob"
+	"encoding/json"
+	"encoding/xml"
+	"testing"
+)
+
+var encodingTests = []string{
+	"-539345864568634858364538753846587364875430589374589",
+	"-678645873",
+	"-100",
+	"-2",
+	"-1",
+	"0",
+	"1",
+	"2",
+	"10",
+	"42",
+	"1234567890",
+	"298472983472983471903246121093472394872319615612417471234712061",
+}
+
+func TestIntGobEncoding(t *testing.T) {
+	var medium bytes.Buffer
+	enc := gob.NewEncoder(&medium)
+	dec := gob.NewDecoder(&medium)
+	for _, test := range encodingTests {
+		medium.Reset() // empty buffer for each test case (in case of failures)
+		var tx Int
+		tx.SetString(test, 10)
+		if err := enc.Encode(&tx); err != nil {
+			t.Errorf("encoding of %s failed: %s", &tx, err)
+		}
+		var rx Int
+		if err := dec.Decode(&rx); err != nil {
+			t.Errorf("decoding of %s failed: %s", &tx, err)
+		}
+		if rx.Cmp(&tx) != 0 {
+			t.Errorf("transmission of %s failed: got %s want %s", &tx, &rx, &tx)
+		}
+	}
+}
+
+// Sending a nil Int pointer (inside a slice) on a round trip through gob should yield a zero.
+// TODO: top-level nils.
+func TestGobEncodingNilIntInSlice(t *testing.T) {
+	buf := new(bytes.Buffer)
+	enc := gob.NewEncoder(buf)
+	dec := gob.NewDecoder(buf)
+
+	var in = make([]*Int, 1)
+	err := enc.Encode(&in)
+	if err != nil {
+		t.Errorf("gob encode failed: %q", err)
+	}
+	var out []*Int
+	err = dec.Decode(&out)
+	if err != nil {
+		t.Fatalf("gob decode failed: %q", err)
+	}
+	if len(out) != 1 {
+		t.Fatalf("wrong len; want 1 got %d", len(out))
+	}
+	var zero Int
+	if out[0].Cmp(&zero) != 0 {
+		t.Errorf("transmission of (*Int)(nill) failed: got %s want 0", out)
+	}
+}
+
+func TestIntJSONEncoding(t *testing.T) {
+	for _, test := range encodingTests {
+		var tx Int
+		tx.SetString(test, 10)
+		b, err := json.Marshal(&tx)
+		if err != nil {
+			t.Errorf("marshaling of %s failed: %s", &tx, err)
+		}
+		var rx Int
+		if err := json.Unmarshal(b, &rx); err != nil {
+			t.Errorf("unmarshaling of %s failed: %s", &tx, err)
+		}
+		if rx.Cmp(&tx) != 0 {
+			t.Errorf("JSON encoding of %s failed: got %s want %s", &tx, &rx, &tx)
+		}
+	}
+}
+
+var intVals = []string{
+	"-141592653589793238462643383279502884197169399375105820974944592307816406286",
+	"-1415926535897932384626433832795028841971",
+	"-141592653589793",
+	"-1",
+	"0",
+	"1",
+	"141592653589793",
+	"1415926535897932384626433832795028841971",
+	"141592653589793238462643383279502884197169399375105820974944592307816406286",
+}
+
+func TestIntJSONEncodingTextMarshaller(t *testing.T) {
+	for _, num := range intVals {
+		var tx Int
+		tx.SetString(num, 0)
+		b, err := json.Marshal(&tx)
+		if err != nil {
+			t.Errorf("marshaling of %s failed: %s", &tx, err)
+			continue
+		}
+		var rx Int
+		if err := json.Unmarshal(b, &rx); err != nil {
+			t.Errorf("unmarshaling of %s failed: %s", &tx, err)
+			continue
+		}
+		if rx.Cmp(&tx) != 0 {
+			t.Errorf("JSON encoding of %s failed: got %s want %s", &tx, &rx, &tx)
+		}
+	}
+}
+
+func TestIntXMLEncodingTextMarshaller(t *testing.T) {
+	for _, num := range intVals {
+		var tx Int
+		tx.SetString(num, 0)
+		b, err := xml.Marshal(&tx)
+		if err != nil {
+			t.Errorf("marshaling of %s failed: %s", &tx, err)
+			continue
+		}
+		var rx Int
+		if err := xml.Unmarshal(b, &rx); err != nil {
+			t.Errorf("unmarshaling of %s failed: %s", &tx, err)
+			continue
+		}
+		if rx.Cmp(&tx) != 0 {
+			t.Errorf("XML encoding of %s failed: got %s want %s", &tx, &rx, &tx)
+		}
+	}
+}
diff --git a/src/math/big/rat.go b/src/math/big/rat.go
index fb16f18..2cd9ed0 100644
--- a/src/math/big/rat.go
+++ b/src/math/big/rat.go
@@ -7,8 +7,6 @@
 package big
 
 import (
-	"encoding/binary"
-	"errors"
 	"fmt"
 	"math"
 )
@@ -510,61 +508,3 @@
 	z.a.neg = a.neg != b.neg
 	return z.norm()
 }
-
-// Gob codec version. Permits backward-compatible changes to the encoding.
-const ratGobVersion byte = 1
-
-// GobEncode implements the gob.GobEncoder interface.
-func (x *Rat) GobEncode() ([]byte, error) {
-	if x == nil {
-		return nil, nil
-	}
-	buf := make([]byte, 1+4+(len(x.a.abs)+len(x.b.abs))*_S) // extra bytes for version and sign bit (1), and numerator length (4)
-	i := x.b.abs.bytes(buf)
-	j := x.a.abs.bytes(buf[:i])
-	n := i - j
-	if int(uint32(n)) != n {
-		// this should never happen
-		return nil, errors.New("Rat.GobEncode: numerator too large")
-	}
-	binary.BigEndian.PutUint32(buf[j-4:j], uint32(n))
-	j -= 1 + 4
-	b := ratGobVersion << 1 // make space for sign bit
-	if x.a.neg {
-		b |= 1
-	}
-	buf[j] = b
-	return buf[j:], nil
-}
-
-// GobDecode implements the gob.GobDecoder interface.
-func (z *Rat) GobDecode(buf []byte) error {
-	if len(buf) == 0 {
-		// Other side sent a nil or default value.
-		*z = Rat{}
-		return nil
-	}
-	b := buf[0]
-	if b>>1 != ratGobVersion {
-		return fmt.Errorf("Rat.GobDecode: encoding version %d not supported", b>>1)
-	}
-	const j = 1 + 4
-	i := j + binary.BigEndian.Uint32(buf[j-4:j])
-	z.a.neg = b&1 != 0
-	z.a.abs = z.a.abs.setBytes(buf[j:i])
-	z.b.abs = z.b.abs.setBytes(buf[i:])
-	return nil
-}
-
-// MarshalText implements the encoding.TextMarshaler interface.
-func (r *Rat) MarshalText() (text []byte, err error) {
-	return []byte(r.RatString()), nil
-}
-
-// UnmarshalText implements the encoding.TextUnmarshaler interface.
-func (r *Rat) UnmarshalText(text []byte) error {
-	if _, ok := r.SetString(string(text)); !ok {
-		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Rat", text)
-	}
-	return nil
-}
diff --git a/src/math/big/rat_test.go b/src/math/big/rat_test.go
index 012d0c4..3a06fca 100644
--- a/src/math/big/rat_test.go
+++ b/src/math/big/rat_test.go
@@ -5,10 +5,6 @@
 package big
 
 import (
-	"bytes"
-	"encoding/gob"
-	"encoding/json"
-	"encoding/xml"
 	"math"
 	"testing"
 )
@@ -280,116 +276,6 @@
 	}
 }
 
-func TestRatGobEncoding(t *testing.T) {
-	var medium bytes.Buffer
-	enc := gob.NewEncoder(&medium)
-	dec := gob.NewDecoder(&medium)
-	for _, test := range encodingTests {
-		medium.Reset() // empty buffer for each test case (in case of failures)
-		var tx Rat
-		tx.SetString(test + ".14159265")
-		if err := enc.Encode(&tx); err != nil {
-			t.Errorf("encoding of %s failed: %s", &tx, err)
-		}
-		var rx Rat
-		if err := dec.Decode(&rx); err != nil {
-			t.Errorf("decoding of %s failed: %s", &tx, err)
-		}
-		if rx.Cmp(&tx) != 0 {
-			t.Errorf("transmission of %s failed: got %s want %s", &tx, &rx, &tx)
-		}
-	}
-}
-
-// Sending a nil Rat pointer (inside a slice) on a round trip through gob should yield a zero.
-// TODO: top-level nils.
-func TestGobEncodingNilRatInSlice(t *testing.T) {
-	buf := new(bytes.Buffer)
-	enc := gob.NewEncoder(buf)
-	dec := gob.NewDecoder(buf)
-
-	var in = make([]*Rat, 1)
-	err := enc.Encode(&in)
-	if err != nil {
-		t.Errorf("gob encode failed: %q", err)
-	}
-	var out []*Rat
-	err = dec.Decode(&out)
-	if err != nil {
-		t.Fatalf("gob decode failed: %q", err)
-	}
-	if len(out) != 1 {
-		t.Fatalf("wrong len; want 1 got %d", len(out))
-	}
-	var zero Rat
-	if out[0].Cmp(&zero) != 0 {
-		t.Errorf("transmission of (*Int)(nill) failed: got %s want 0", out)
-	}
-}
-
-var ratNums = []string{
-	"-141592653589793238462643383279502884197169399375105820974944592307816406286",
-	"-1415926535897932384626433832795028841971",
-	"-141592653589793",
-	"-1",
-	"0",
-	"1",
-	"141592653589793",
-	"1415926535897932384626433832795028841971",
-	"141592653589793238462643383279502884197169399375105820974944592307816406286",
-}
-
-var ratDenoms = []string{
-	"1",
-	"718281828459045",
-	"7182818284590452353602874713526624977572",
-	"718281828459045235360287471352662497757247093699959574966967627724076630353",
-}
-
-func TestRatJSONEncoding(t *testing.T) {
-	for _, num := range ratNums {
-		for _, denom := range ratDenoms {
-			var tx Rat
-			tx.SetString(num + "/" + denom)
-			b, err := json.Marshal(&tx)
-			if err != nil {
-				t.Errorf("marshaling of %s failed: %s", &tx, err)
-				continue
-			}
-			var rx Rat
-			if err := json.Unmarshal(b, &rx); err != nil {
-				t.Errorf("unmarshaling of %s failed: %s", &tx, err)
-				continue
-			}
-			if rx.Cmp(&tx) != 0 {
-				t.Errorf("JSON encoding of %s failed: got %s want %s", &tx, &rx, &tx)
-			}
-		}
-	}
-}
-
-func TestRatXMLEncoding(t *testing.T) {
-	for _, num := range ratNums {
-		for _, denom := range ratDenoms {
-			var tx Rat
-			tx.SetString(num + "/" + denom)
-			b, err := xml.Marshal(&tx)
-			if err != nil {
-				t.Errorf("marshaling of %s failed: %s", &tx, err)
-				continue
-			}
-			var rx Rat
-			if err := xml.Unmarshal(b, &rx); err != nil {
-				t.Errorf("unmarshaling of %s failed: %s", &tx, err)
-				continue
-			}
-			if rx.Cmp(&tx) != 0 {
-				t.Errorf("XML encoding of %s failed: got %s want %s", &tx, &rx, &tx)
-			}
-		}
-	}
-}
-
 func TestIssue2379(t *testing.T) {
 	// 1) no aliasing
 	q := NewRat(3, 2)
diff --git a/src/math/big/ratmarsh.go b/src/math/big/ratmarsh.go
new file mode 100644
index 0000000..b79cbe6
--- /dev/null
+++ b/src/math/big/ratmarsh.go
@@ -0,0 +1,71 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements encoding/decoding of Rats.
+
+package big
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+)
+
+// Gob codec version. Permits backward-compatible changes to the encoding.
+const ratGobVersion byte = 1
+
+// GobEncode implements the gob.GobEncoder interface.
+func (x *Rat) GobEncode() ([]byte, error) {
+	if x == nil {
+		return nil, nil
+	}
+	buf := make([]byte, 1+4+(len(x.a.abs)+len(x.b.abs))*_S) // extra bytes for version and sign bit (1), and numerator length (4)
+	i := x.b.abs.bytes(buf)
+	j := x.a.abs.bytes(buf[:i])
+	n := i - j
+	if int(uint32(n)) != n {
+		// this should never happen
+		return nil, errors.New("Rat.GobEncode: numerator too large")
+	}
+	binary.BigEndian.PutUint32(buf[j-4:j], uint32(n))
+	j -= 1 + 4
+	b := ratGobVersion << 1 // make space for sign bit
+	if x.a.neg {
+		b |= 1
+	}
+	buf[j] = b
+	return buf[j:], nil
+}
+
+// GobDecode implements the gob.GobDecoder interface.
+func (z *Rat) GobDecode(buf []byte) error {
+	if len(buf) == 0 {
+		// Other side sent a nil or default value.
+		*z = Rat{}
+		return nil
+	}
+	b := buf[0]
+	if b>>1 != ratGobVersion {
+		return fmt.Errorf("Rat.GobDecode: encoding version %d not supported", b>>1)
+	}
+	const j = 1 + 4
+	i := j + binary.BigEndian.Uint32(buf[j-4:j])
+	z.a.neg = b&1 != 0
+	z.a.abs = z.a.abs.setBytes(buf[j:i])
+	z.b.abs = z.b.abs.setBytes(buf[i:])
+	return nil
+}
+
+// MarshalText implements the encoding.TextMarshaler interface.
+func (r *Rat) MarshalText() (text []byte, err error) {
+	return []byte(r.RatString()), nil
+}
+
+// UnmarshalText implements the encoding.TextUnmarshaler interface.
+func (r *Rat) UnmarshalText(text []byte) error {
+	if _, ok := r.SetString(string(text)); !ok {
+		return fmt.Errorf("math/big: cannot unmarshal %q into a *big.Rat", text)
+	}
+	return nil
+}
diff --git a/src/math/big/ratmarsh_test.go b/src/math/big/ratmarsh_test.go
new file mode 100644
index 0000000..2e91e38
--- /dev/null
+++ b/src/math/big/ratmarsh_test.go
@@ -0,0 +1,123 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package big
+
+import (
+	"bytes"
+	"encoding/gob"
+	"encoding/json"
+	"encoding/xml"
+	"testing"
+)
+
+func TestRatGobEncoding(t *testing.T) {
+	var medium bytes.Buffer
+	enc := gob.NewEncoder(&medium)
+	dec := gob.NewDecoder(&medium)
+	for _, test := range encodingTests {
+		medium.Reset() // empty buffer for each test case (in case of failures)
+		var tx Rat
+		tx.SetString(test + ".14159265")
+		if err := enc.Encode(&tx); err != nil {
+			t.Errorf("encoding of %s failed: %s", &tx, err)
+		}
+		var rx Rat
+		if err := dec.Decode(&rx); err != nil {
+			t.Errorf("decoding of %s failed: %s", &tx, err)
+		}
+		if rx.Cmp(&tx) != 0 {
+			t.Errorf("transmission of %s failed: got %s want %s", &tx, &rx, &tx)
+		}
+	}
+}
+
+// Sending a nil Rat pointer (inside a slice) on a round trip through gob should yield a zero.
+// TODO: top-level nils.
+func TestGobEncodingNilRatInSlice(t *testing.T) {
+	buf := new(bytes.Buffer)
+	enc := gob.NewEncoder(buf)
+	dec := gob.NewDecoder(buf)
+
+	var in = make([]*Rat, 1)
+	err := enc.Encode(&in)
+	if err != nil {
+		t.Errorf("gob encode failed: %q", err)
+	}
+	var out []*Rat
+	err = dec.Decode(&out)
+	if err != nil {
+		t.Fatalf("gob decode failed: %q", err)
+	}
+	if len(out) != 1 {
+		t.Fatalf("wrong len; want 1 got %d", len(out))
+	}
+	var zero Rat
+	if out[0].Cmp(&zero) != 0 {
+		t.Errorf("transmission of (*Int)(nill) failed: got %s want 0", out)
+	}
+}
+
+var ratNums = []string{
+	"-141592653589793238462643383279502884197169399375105820974944592307816406286",
+	"-1415926535897932384626433832795028841971",
+	"-141592653589793",
+	"-1",
+	"0",
+	"1",
+	"141592653589793",
+	"1415926535897932384626433832795028841971",
+	"141592653589793238462643383279502884197169399375105820974944592307816406286",
+}
+
+var ratDenoms = []string{
+	"1",
+	"718281828459045",
+	"7182818284590452353602874713526624977572",
+	"718281828459045235360287471352662497757247093699959574966967627724076630353",
+}
+
+func TestRatJSONEncoding(t *testing.T) {
+	for _, num := range ratNums {
+		for _, denom := range ratDenoms {
+			var tx Rat
+			tx.SetString(num + "/" + denom)
+			b, err := json.Marshal(&tx)
+			if err != nil {
+				t.Errorf("marshaling of %s failed: %s", &tx, err)
+				continue
+			}
+			var rx Rat
+			if err := json.Unmarshal(b, &rx); err != nil {
+				t.Errorf("unmarshaling of %s failed: %s", &tx, err)
+				continue
+			}
+			if rx.Cmp(&tx) != 0 {
+				t.Errorf("JSON encoding of %s failed: got %s want %s", &tx, &rx, &tx)
+			}
+		}
+	}
+}
+
+func TestRatXMLEncoding(t *testing.T) {
+	for _, num := range ratNums {
+		for _, denom := range ratDenoms {
+			var tx Rat
+			tx.SetString(num + "/" + denom)
+			b, err := xml.Marshal(&tx)
+			if err != nil {
+				t.Errorf("marshaling of %s failed: %s", &tx, err)
+				continue
+			}
+			var rx Rat
+			if err := xml.Unmarshal(b, &rx); err != nil {
+				t.Errorf("unmarshaling of %s failed: %s", &tx, err)
+				continue
+			}
+			if rx.Cmp(&tx) != 0 {
+				t.Errorf("XML encoding of %s failed: got %s want %s", &tx, &rx, &tx)
+			}
+		}
+	}
+}