diff --git a/parser/types.go b/parser/types.go
index e5d7937..9e67eaa 100644
--- a/parser/types.go
+++ b/parser/types.go
@@ -7,90 +7,91 @@ package parser
 import "fmt"
 
 type Type struct {
-	Name        string
-	KeyType     *Type // If map
-	ValueType   *Type // If map, list, or set
-	Annotations []*Annotation
+	Name        string        `json:"name,omitempty"`
+	KeyType     *Type         `json:"key_type,omitempty"`   // If map
+	ValueType   *Type         `json:"value_type,omitempty"` // If map, list, or set
+	Annotations []*Annotation `json:"annotations,omitempty"`
 }
 
 type Typedef struct {
 	*Type
 
-	Alias       string
-	Annotations []*Annotation
+	Alias       string        `json:"alias"`
+	Annotations []*Annotation `json:"annotations,omitempty"`
 }
 
 type EnumValue struct {
-	Name        string
-	Value       int
-	Annotations []*Annotation
+	Name        string        `json:"name"`
+	Value       int           `json:"value"`
+	Annotations []*Annotation `json:"annotations,omitempty"`
 }
 
 type Enum struct {
-	Name        string
-	Values      map[string]*EnumValue
-	Annotations []*Annotation
+	Name        string                `json:"name"`
+	Values      map[string]*EnumValue `json:"values"`
+	Annotations []*Annotation         `json:"annotations,omitempty"`
 }
 
 type Constant struct {
-	Name  string
-	Type  *Type
+	Name  string `json:"name"`
+	Type  *Type  `json:"type"`
 	Value interface{}
 }
 
 type Field struct {
-	ID          int
-	Name        string
-	Optional    bool
-	Type        *Type
-	Default     interface{}
-	Annotations []*Annotation
+	ID          int           `json:"id"`
+	Name        string        `json:"name"`
+	Optional    bool          `json:"optional"`
+	Type        *Type         `json:"type"`
+	Default     interface{}   `json:"default,omitempty"`
+	Annotations []*Annotation `json:"annotations,omitempty"`
 }
 
 type Struct struct {
-	Name        string
-	Fields      []*Field
-	Annotations []*Annotation
+	Name        string        `json:"name"`
+	Fields      []*Field      `json:"fields"`
+	Annotations []*Annotation `json:"annotations,omitempty"`
 }
 
 type Method struct {
-	Comment     string
-	Name        string
-	Oneway      bool
-	ReturnType  *Type
-	Arguments   []*Field
-	Exceptions  []*Field
-	Annotations []*Annotation
+	Comment     string        `json:"comment"`
+	Name        string        `json:"name"`
+	Oneway      bool          `json:"one_way"`
+	ReturnType  *Type         `json:"return_type"`
+	Arguments   []*Field      `json:"arguments"`
+	Exceptions  []*Field      `json:"exceptions,omitempty"`
+	Annotations []*Annotation `json:"annotations,omitempty"`
 }
 
 type Service struct {
-	Name        string
-	Extends     string
-	Methods     map[string]*Method
-	Annotations []*Annotation
+	Name        string             `json:"name"`
+	Extends     string             `json:"extends,omitempty"`
+	Methods     map[string]*Method `json:"methods"`
+	Annotations []*Annotation      `json:"annotations,omitempty"`
 }
 
 type Thrift struct {
-	Includes   map[string]string // name -> unique identifier (absolute path generally)
-	Typedefs   map[string]*Typedef
-	Namespaces map[string]string
-	Constants  map[string]*Constant
-	Enums      map[string]*Enum
-	Structs    map[string]*Struct
-	Exceptions map[string]*Struct
-	Unions     map[string]*Struct
-	Services   map[string]*Service
+	Includes   map[string]string    `json:"includes,omitempty"` // name -> unique identifier (absolute path generally)
+	Typedefs   map[string]*Typedef  `json:"typedefs,omitempty"`
+	Namespaces map[string]string    `json:"namespaces,omitempty"`
+	Constants  map[string]*Constant `json:"constants,omitempty"`
+	Enums      map[string]*Enum     `json:"enums,omitempty"`
+	Structs    map[string]*Struct   `json:"structs,omitempty"`
+	Exceptions map[string]*Struct   `json:"exceptions,omitempty"`
+	Unions     map[string]*Struct   `json:"unions,omitempty"`
+	Services   map[string]*Service  `json:"services,omitempty"`
 }
 
 type Identifier string
 
 type KeyValue struct {
-	Key, Value interface{}
+	Key   interface{} `json:"key"`
+	Value interface{} `json:"value"`
 }
 
 type Annotation struct {
-	Name  string
-	Value string
+	Name  string `json:"name"`
+	Value string `json:"value"`
 }
 
 func (t *Type) String() string {
diff --git a/thrift/decoder.go b/thrift/decoder.go
index 3ccd88e..90bef85 100644
--- a/thrift/decoder.go
+++ b/thrift/decoder.go
@@ -142,7 +142,7 @@ func (d *decoder) readValue(thriftType byte, rf reflect.Value) {
 		}
 
 		meta := encodeFields(v.Type())
-		req := meta.required
+		req := meta.required.Clone()
 		for {
 			ftype, id, err := d.r.ReadFieldBegin()
 			if err != nil {
@@ -156,7 +156,7 @@ func (d *decoder) readValue(thriftType byte, rf reflect.Value) {
 			if !ok {
 				SkipValue(d.r, ftype)
 			} else {
-				req &= ^(uint64(1) << uint64(id))
+				req.Clear(uint(id))
 				fieldValue := v.Field(ef.i)
 				if ftype != ef.fieldType {
 					d.error(&UnsupportedValueError{Value: fieldValue, Str: "type mismatch"})
@@ -173,14 +173,12 @@ func (d *decoder) readValue(thriftType byte, rf reflect.Value) {
 			d.error(err)
 		}
 
-		if req != 0 {
-			for i := 0; req != 0; i, req = i+1, req>>1 {
-				if req&1 != 0 {
-					d.error(&MissingRequiredField{
-						StructName: v.Type().Name(),
-						FieldName:  meta.fields[i].name,
-					})
-				}
+		if req.Count() > 0 {
+			for i, e := req.NextSet(0); e; i, e = req.NextSet(i + 1) {
+				d.error(&MissingRequiredField{
+					StructName: v.Type().Name(),
+					FieldName:  meta.fields[int(i)].name,
+				})
 			}
 		}
 	case TypeMap:
diff --git a/thrift/thrift.go b/thrift/thrift.go
index 8a15f93..9936b9b 100644
--- a/thrift/thrift.go
+++ b/thrift/thrift.go
@@ -10,6 +10,8 @@ import (
 	"reflect"
 	"sort"
 	"sync"
+
+	"github.com/willf/bitset"
 )
 
 // Type identifiers for serialized Thrift
@@ -201,7 +203,7 @@ type encodeField struct {
 }
 
 type structMeta struct {
-	required   uint64 // bitmap of required fields
+	required   *bitset.BitSet // bitmap of required fields
 	orderedIds []int
 	fields     map[int]encodeField
 }
@@ -229,7 +231,7 @@ func encodeFields(t reflect.Type) structMeta {
 	}
 
 	fs := make(map[int]encodeField)
-	m = structMeta{fields: fs}
+	m = structMeta{fields: fs, required: bitset.New(64)}
 	v := reflect.Zero(t)
 	n := v.NumField()
 	for i := 0; i < n; i++ {
@@ -260,7 +262,7 @@ func encodeFields(t reflect.Type) structMeta {
 			ef.name = f.Name
 			ef.required = opts.Contains("required")
 			if ef.required {
-				m.required |= 1 << byte(id)
+				m.required.Set(uint(id))
 			}
 			ef.keepEmpty = opts.Contains("keepempty")
 			if opts.Contains("set") {