diff --git a/jsonpb/jsonpb.go b/jsonpb/jsonpb.go
index 6308548..e40d1d3 100644
--- a/jsonpb/jsonpb.go
+++ b/jsonpb/jsonpb.go
@@ -510,41 +510,63 @@
 	return out.err
 }
 
+// Unmarshaler is a configurable object for converting from a JSON
+// representation to a protocol buffer object.
+type Unmarshaler struct {
+	// Whether to allow messages to contain unknown fields, as opposed to
+	// failing to unmarshal.
+	AllowUnknownFields bool
+}
+
 // UnmarshalNext unmarshals the next protocol buffer from a JSON object stream.
 // This function is lenient and will decode any options permutations of the
 // related Marshaler.
-func UnmarshalNext(dec *json.Decoder, pb proto.Message) error {
+func (u *Unmarshaler) UnmarshalNext(dec *json.Decoder, pb proto.Message) error {
 	inputValue := json.RawMessage{}
 	if err := dec.Decode(&inputValue); err != nil {
 		return err
 	}
-	return unmarshalValue(reflect.ValueOf(pb).Elem(), inputValue, nil)
+	return u.unmarshalValue(reflect.ValueOf(pb).Elem(), inputValue, nil)
+}
+
+// Unmarshal unmarshals a JSON object stream into a protocol
+// buffer. This function is lenient and will decode any options
+// permutations of the related Marshaler.
+func (u *Unmarshaler) Unmarshal(r io.Reader, pb proto.Message) error {
+	dec := json.NewDecoder(r)
+	return u.UnmarshalNext(dec, pb)
+}
+
+// UnmarshalNext unmarshals the next protocol buffer from a JSON object stream.
+// This function is lenient and will decode any options permutations of the
+// related Marshaler.
+func UnmarshalNext(dec *json.Decoder, pb proto.Message) error {
+	return new(Unmarshaler).UnmarshalNext(dec, pb)
 }
 
 // Unmarshal unmarshals a JSON object stream into a protocol
 // buffer. This function is lenient and will decode any options
 // permutations of the related Marshaler.
 func Unmarshal(r io.Reader, pb proto.Message) error {
-	dec := json.NewDecoder(r)
-	return UnmarshalNext(dec, pb)
+	return new(Unmarshaler).Unmarshal(r, pb)
 }
 
 // UnmarshalString will populate the fields of a protocol buffer based
 // on a JSON string. This function is lenient and will decode any options
 // permutations of the related Marshaler.
 func UnmarshalString(str string, pb proto.Message) error {
-	return Unmarshal(strings.NewReader(str), pb)
+	return new(Unmarshaler).Unmarshal(strings.NewReader(str), pb)
 }
 
 // unmarshalValue converts/copies a value into the target.
 // prop may be nil.
-func unmarshalValue(target reflect.Value, inputValue json.RawMessage, prop *proto.Properties) error {
+func (u *Unmarshaler) unmarshalValue(target reflect.Value, inputValue json.RawMessage, prop *proto.Properties) error {
 	targetType := target.Type()
 
 	// Allocate memory for pointer fields.
 	if targetType.Kind() == reflect.Ptr {
 		target.Set(reflect.New(targetType.Elem()))
-		return unmarshalValue(target.Elem(), inputValue, prop)
+		return u.unmarshalValue(target.Elem(), inputValue, prop)
 	}
 
 	// Handle well-known types.
@@ -559,7 +581,7 @@
 			//  as the wrapped primitive type, except that null is allowed."
 			// encoding/json will turn JSON `null` into Go `nil`,
 			// so we don't have to do any extra work.
-			return unmarshalValue(target.Field(0), inputValue, prop)
+			return u.unmarshalValue(target.Field(0), inputValue, prop)
 		case "Any":
 			return fmt.Errorf("unmarshaling Any not supported yet")
 		case "Duration":
@@ -657,7 +679,7 @@
 				continue
 			}
 
-			if err := unmarshalValue(target.Field(i), valueForField, sprops.Prop[i]); err != nil {
+			if err := u.unmarshalValue(target.Field(i), valueForField, sprops.Prop[i]); err != nil {
 				return err
 			}
 		}
@@ -670,12 +692,12 @@
 				}
 				nv := reflect.New(oop.Type.Elem())
 				target.Field(oop.Field).Set(nv)
-				if err := unmarshalValue(nv.Elem().Field(0), raw, oop.Prop); err != nil {
+				if err := u.unmarshalValue(nv.Elem().Field(0), raw, oop.Prop); err != nil {
 					return err
 				}
 			}
 		}
-		if len(jsonFields) > 0 {
+		if !u.AllowUnknownFields && len(jsonFields) > 0 {
 			// Pick any field to be the scapegoat.
 			var f string
 			for fname := range jsonFields {
@@ -696,7 +718,7 @@
 		len := len(slc)
 		target.Set(reflect.MakeSlice(targetType, len, len))
 		for i := 0; i < len; i++ {
-			if err := unmarshalValue(target.Index(i), slc[i], prop); err != nil {
+			if err := u.unmarshalValue(target.Index(i), slc[i], prop); err != nil {
 				return err
 			}
 		}
@@ -725,14 +747,14 @@
 				k = reflect.ValueOf(ks)
 			} else {
 				k = reflect.New(targetType.Key()).Elem()
-				if err := unmarshalValue(k, json.RawMessage(ks), keyprop); err != nil {
+				if err := u.unmarshalValue(k, json.RawMessage(ks), keyprop); err != nil {
 					return err
 				}
 			}
 
 			// Unmarshal map value.
 			v := reflect.New(targetType.Elem()).Elem()
-			if err := unmarshalValue(v, raw, valprop); err != nil {
+			if err := u.unmarshalValue(v, raw, valprop); err != nil {
 				return err
 			}
 			target.SetMapIndex(k, v)
diff --git a/jsonpb/jsonpb_test.go b/jsonpb/jsonpb_test.go
index 659dbed..8cbc8ec 100644
--- a/jsonpb/jsonpb_test.go
+++ b/jsonpb/jsonpb_test.go
@@ -36,6 +36,7 @@
 	"encoding/json"
 	"io"
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/golang/protobuf/proto"
@@ -410,66 +411,69 @@
 }
 
 var unmarshalingTests = []struct {
-	desc string
-	json string
-	pb   proto.Message
+	desc        string
+	unmarshaler Unmarshaler
+	json        string
+	pb          proto.Message
 }{
-	{"simple flat object", simpleObjectJSON, simpleObject},
-	{"simple pretty object", simpleObjectPrettyJSON, simpleObject},
-	{"repeated fields flat object", repeatsObjectJSON, repeatsObject},
-	{"repeated fields pretty object", repeatsObjectPrettyJSON, repeatsObject},
-	{"nested message/enum flat object", complexObjectJSON, complexObject},
-	{"nested message/enum pretty object", complexObjectPrettyJSON, complexObject},
-	{"enum-string object", `{"color":"BLUE"}`, &pb.Widget{Color: pb.Widget_BLUE.Enum()}},
-	{"enum-value object", "{\n \"color\": 2\n}", &pb.Widget{Color: pb.Widget_BLUE.Enum()}},
-	{"proto3 enum string", `{"hilarity":"PUNS"}`, &proto3pb.Message{Hilarity: proto3pb.Message_PUNS}},
-	{"proto3 enum value", `{"hilarity":1}`, &proto3pb.Message{Hilarity: proto3pb.Message_PUNS}},
+	{"simple flat object", Unmarshaler{}, simpleObjectJSON, simpleObject},
+	{"simple pretty object", Unmarshaler{}, simpleObjectPrettyJSON, simpleObject},
+	{"repeated fields flat object", Unmarshaler{}, repeatsObjectJSON, repeatsObject},
+	{"repeated fields pretty object", Unmarshaler{}, repeatsObjectPrettyJSON, repeatsObject},
+	{"nested message/enum flat object", Unmarshaler{}, complexObjectJSON, complexObject},
+	{"nested message/enum pretty object", Unmarshaler{}, complexObjectPrettyJSON, complexObject},
+	{"enum-string object", Unmarshaler{}, `{"color":"BLUE"}`, &pb.Widget{Color: pb.Widget_BLUE.Enum()}},
+	{"enum-value object", Unmarshaler{}, "{\n \"color\": 2\n}", &pb.Widget{Color: pb.Widget_BLUE.Enum()}},
+	{"unknown field with allowed option", Unmarshaler{AllowUnknownFields: true}, `{"unknown": "foo"}`, new(pb.Simple)},
+	{"proto3 enum string", Unmarshaler{}, `{"hilarity":"PUNS"}`, &proto3pb.Message{Hilarity: proto3pb.Message_PUNS}},
+	{"proto3 enum value", Unmarshaler{}, `{"hilarity":1}`, &proto3pb.Message{Hilarity: proto3pb.Message_PUNS}},
 	{"unknown enum value object",
+		Unmarshaler{},
 		"{\n  \"color\": 1000,\n  \"r_color\": [\n    \"RED\"\n  ]\n}",
 		&pb.Widget{Color: pb.Widget_Color(1000).Enum(), RColor: []pb.Widget_Color{pb.Widget_RED}}},
-	{"repeated proto3 enum", `{"rFunny":["PUNS","SLAPSTICK"]}`,
+	{"repeated proto3 enum", Unmarshaler{}, `{"rFunny":["PUNS","SLAPSTICK"]}`,
 		&proto3pb.Message{RFunny: []proto3pb.Message_Humour{
 			proto3pb.Message_PUNS,
 			proto3pb.Message_SLAPSTICK,
 		}}},
-	{"repeated proto3 enum as int", `{"rFunny":[1,2]}`,
+	{"repeated proto3 enum as int", Unmarshaler{}, `{"rFunny":[1,2]}`,
 		&proto3pb.Message{RFunny: []proto3pb.Message_Humour{
 			proto3pb.Message_PUNS,
 			proto3pb.Message_SLAPSTICK,
 		}}},
-	{"repeated proto3 enum as mix of strings and ints", `{"rFunny":["PUNS",2]}`,
+	{"repeated proto3 enum as mix of strings and ints", Unmarshaler{}, `{"rFunny":["PUNS",2]}`,
 		&proto3pb.Message{RFunny: []proto3pb.Message_Humour{
 			proto3pb.Message_PUNS,
 			proto3pb.Message_SLAPSTICK,
 		}}},
-	{"unquoted int64 object", `{"oInt64":-314}`, &pb.Simple{OInt64: proto.Int64(-314)}},
-	{"unquoted uint64 object", `{"oUint64":123}`, &pb.Simple{OUint64: proto.Uint64(123)}},
-	{"map<int64, int32>", `{"nummy":{"1":2,"3":4}}`, &pb.Mappy{Nummy: map[int64]int32{1: 2, 3: 4}}},
-	{"map<string, string>", `{"strry":{"\"one\"":"two","three":"four"}}`, &pb.Mappy{Strry: map[string]string{`"one"`: "two", "three": "four"}}},
-	{"map<int32, Object>", `{"objjy":{"1":{"dub":1}}}`, &pb.Mappy{Objjy: map[int32]*pb.Simple3{1: &pb.Simple3{Dub: 1}}}},
+	{"unquoted int64 object", Unmarshaler{}, `{"oInt64":-314}`, &pb.Simple{OInt64: proto.Int64(-314)}},
+	{"unquoted uint64 object", Unmarshaler{}, `{"oUint64":123}`, &pb.Simple{OUint64: proto.Uint64(123)}},
+	{"map<int64, int32>", Unmarshaler{}, `{"nummy":{"1":2,"3":4}}`, &pb.Mappy{Nummy: map[int64]int32{1: 2, 3: 4}}},
+	{"map<string, string>", Unmarshaler{}, `{"strry":{"\"one\"":"two","three":"four"}}`, &pb.Mappy{Strry: map[string]string{`"one"`: "two", "three": "four"}}},
+	{"map<int32, Object>", Unmarshaler{}, `{"objjy":{"1":{"dub":1}}}`, &pb.Mappy{Objjy: map[int32]*pb.Simple3{1: &pb.Simple3{Dub: 1}}}},
 	// TODO: This is broken.
-	//{"map<string, enum>", `{"enumy":{"XIV":"ROMAN"}`, &pb.Mappy{Enumy: map[string]pb.Numeral{"XIV": pb.Numeral_ROMAN}}},
-	{"map<string, enum as int>", `{"enumy":{"XIV":2}}`, &pb.Mappy{Enumy: map[string]pb.Numeral{"XIV": pb.Numeral_ROMAN}}},
-	{"oneof", `{"salary":31000}`, &pb.MsgWithOneof{Union: &pb.MsgWithOneof_Salary{31000}}},
-	{"oneof spec name", `{"country":"Australia"}`, &pb.MsgWithOneof{Union: &pb.MsgWithOneof_Country{"Australia"}}},
-	{"oneof orig_name", `{"Country":"Australia"}`, &pb.MsgWithOneof{Union: &pb.MsgWithOneof_Country{"Australia"}}},
-	{"orig_name input", `{"o_bool":true}`, &pb.Simple{OBool: proto.Bool(true)}},
-	{"camelName input", `{"oBool":true}`, &pb.Simple{OBool: proto.Bool(true)}},
+	//{"map<string, enum>", Unmarshaler{}, `{"enumy":{"XIV":"ROMAN"}`, &pb.Mappy{Enumy: map[string]pb.Numeral{"XIV": pb.Numeral_ROMAN}}},
+	{"map<string, enum as int>", Unmarshaler{}, `{"enumy":{"XIV":2}}`, &pb.Mappy{Enumy: map[string]pb.Numeral{"XIV": pb.Numeral_ROMAN}}},
+	{"oneof", Unmarshaler{}, `{"salary":31000}`, &pb.MsgWithOneof{Union: &pb.MsgWithOneof_Salary{31000}}},
+	{"oneof spec name", Unmarshaler{}, `{"country":"Australia"}`, &pb.MsgWithOneof{Union: &pb.MsgWithOneof_Country{"Australia"}}},
+	{"oneof orig_name", Unmarshaler{}, `{"Country":"Australia"}`, &pb.MsgWithOneof{Union: &pb.MsgWithOneof_Country{"Australia"}}},
+	{"orig_name input", Unmarshaler{}, `{"o_bool":true}`, &pb.Simple{OBool: proto.Bool(true)}},
+	{"camelName input", Unmarshaler{}, `{"oBool":true}`, &pb.Simple{OBool: proto.Bool(true)}},
 
-	{"Duration", `{"dur":"3.000s"}`, &pb.KnownTypes{Dur: &durpb.Duration{Seconds: 3}}},
-	{"Timestamp", `{"ts":"2014-05-13T16:53:20.021Z"}`, &pb.KnownTypes{Ts: &tspb.Timestamp{Seconds: 14e8, Nanos: 21e6}}},
+	{"Duration", Unmarshaler{}, `{"dur":"3.000s"}`, &pb.KnownTypes{Dur: &durpb.Duration{Seconds: 3}}},
+	{"Timestamp", Unmarshaler{}, `{"ts":"2014-05-13T16:53:20.021Z"}`, &pb.KnownTypes{Ts: &tspb.Timestamp{Seconds: 14e8, Nanos: 21e6}}},
 
-	{"DoubleValue", `{"dbl":1.2}`, &pb.KnownTypes{Dbl: &wpb.DoubleValue{Value: 1.2}}},
-	{"FloatValue", `{"flt":1.2}`, &pb.KnownTypes{Flt: &wpb.FloatValue{Value: 1.2}}},
-	{"Int64Value", `{"i64":"-3"}`, &pb.KnownTypes{I64: &wpb.Int64Value{Value: -3}}},
-	{"UInt64Value", `{"u64":"3"}`, &pb.KnownTypes{U64: &wpb.UInt64Value{Value: 3}}},
-	{"Int32Value", `{"i32":-4}`, &pb.KnownTypes{I32: &wpb.Int32Value{Value: -4}}},
-	{"UInt32Value", `{"u32":4}`, &pb.KnownTypes{U32: &wpb.UInt32Value{Value: 4}}},
-	{"BoolValue", `{"bool":true}`, &pb.KnownTypes{Bool: &wpb.BoolValue{Value: true}}},
-	{"StringValue", `{"str":"plush"}`, &pb.KnownTypes{Str: &wpb.StringValue{Value: "plush"}}},
-	{"BytesValue", `{"bytes":"d293"}`, &pb.KnownTypes{Bytes: &wpb.BytesValue{Value: []byte("wow")}}},
+	{"DoubleValue", Unmarshaler{}, `{"dbl":1.2}`, &pb.KnownTypes{Dbl: &wpb.DoubleValue{Value: 1.2}}},
+	{"FloatValue", Unmarshaler{}, `{"flt":1.2}`, &pb.KnownTypes{Flt: &wpb.FloatValue{Value: 1.2}}},
+	{"Int64Value", Unmarshaler{}, `{"i64":"-3"}`, &pb.KnownTypes{I64: &wpb.Int64Value{Value: -3}}},
+	{"UInt64Value", Unmarshaler{}, `{"u64":"3"}`, &pb.KnownTypes{U64: &wpb.UInt64Value{Value: 3}}},
+	{"Int32Value", Unmarshaler{}, `{"i32":-4}`, &pb.KnownTypes{I32: &wpb.Int32Value{Value: -4}}},
+	{"UInt32Value", Unmarshaler{}, `{"u32":4}`, &pb.KnownTypes{U32: &wpb.UInt32Value{Value: 4}}},
+	{"BoolValue", Unmarshaler{}, `{"bool":true}`, &pb.KnownTypes{Bool: &wpb.BoolValue{Value: true}}},
+	{"StringValue", Unmarshaler{}, `{"str":"plush"}`, &pb.KnownTypes{Str: &wpb.StringValue{Value: "plush"}}},
+	{"BytesValue", Unmarshaler{}, `{"bytes":"d293"}`, &pb.KnownTypes{Bytes: &wpb.BytesValue{Value: []byte("wow")}}},
 	// `null` is also a permissible value. Let's just test one.
-	{"null DoubleValue", `{"dbl":null}`, &pb.KnownTypes{Dbl: &wpb.DoubleValue{}}},
+	{"null DoubleValue", Unmarshaler{}, `{"dbl":null}`, &pb.KnownTypes{Dbl: &wpb.DoubleValue{}}},
 }
 
 func TestUnmarshaling(t *testing.T) {
@@ -477,7 +481,7 @@
 		// Make a new instance of the type of our expected object.
 		p := reflect.New(reflect.TypeOf(tt.pb).Elem()).Interface().(proto.Message)
 
-		err := UnmarshalString(tt.json, p)
+		err := tt.unmarshaler.Unmarshal(strings.NewReader(tt.json), p)
 		if err != nil {
 			t.Errorf("%s: %v", tt.desc, err)
 			continue
@@ -507,7 +511,7 @@
 		// Make a new instance of the type of our expected object.
 		p := reflect.New(reflect.TypeOf(tt.pb).Elem()).Interface().(proto.Message)
 
-		err := UnmarshalNext(dec, p)
+		err := tt.unmarshaler.UnmarshalNext(dec, p)
 		if err != nil {
 			t.Errorf("%s: %v", tt.desc, err)
 			continue
@@ -522,7 +526,7 @@
 	}
 
 	p := &pb.Simple{}
-	err := UnmarshalNext(dec, p)
+	err := new(Unmarshaler).UnmarshalNext(dec, p)
 	if err != io.EOF {
 		t.Errorf("eof: got %v, expected io.EOF", err)
 	}
@@ -535,6 +539,7 @@
 }{
 	{"a value", "666", new(pb.Simple)},
 	{"gibberish", "{adskja123;l23=-=", new(pb.Simple)},
+	{"unknown field", `{"unknown": "foo"}`, new(pb.Simple)},
 	{"unknown enum name", `{"hilarity":"DAVE"}`, new(proto3pb.Message)},
 }