diff --git a/example/cmd/main.go b/example/cmd/main.go
index 8c83c2c99..61c0503c4 100644
--- a/example/cmd/main.go
+++ b/example/cmd/main.go
@@ -66,7 +66,7 @@ func dumpMetadata(ctx context.Context) {
 	if !ok {
 		panic("no metadata")
 	}
-	if err := json.NewEncoder(os.Stdout).Encode(md); err != nil {
+	if err := json.NewEncoder(os.Stdout).Encode(md.GetCopy()); err != nil {
 		panic(err)
 	}
 }
@@ -109,7 +109,7 @@ func client() error {
 	}
 
 	ctx := context.Background()
-	md := ttrpc.MD{}
+	md := ttrpc.NewMD(make(map[string][]string))
 	md.Set("name", "koye")
 	ctx = ttrpc.WithMetadata(ctx, md)
 
diff --git a/metadata.go b/metadata.go
index ce8c0d13c..aa58e3bfa 100644
--- a/metadata.go
+++ b/metadata.go
@@ -19,16 +19,30 @@ package ttrpc
 import (
 	"context"
 	"strings"
+	"sync"
 )
 
 // MD is the user type for ttrpc metadata
-type MD map[string][]string
+type MD struct {
+	data map[string][]string
+	mu   sync.RWMutex
+}
+
+// NewMD creates a metadata object.
+func NewMD(data map[string][]string) *MD {
+	return &MD{
+		data: data,
+	}
+}
 
 // Get returns the metadata for a given key when they exist.
 // If there is no metadata, a nil slice and false are returned.
-func (m MD) Get(key string) ([]string, bool) {
+func (m *MD) Get(key string) ([]string, bool) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
 	key = strings.ToLower(key)
-	list, ok := m[key]
+	list, ok := m.data[key]
 	if !ok || len(list) == 0 {
 		return nil, false
 	}
@@ -39,31 +53,54 @@ func (m MD) Get(key string) ([]string, bool) {
 // Set sets the provided values for a given key.
 // The values will overwrite any existing values.
 // If no values provided, a key will be deleted.
-func (m MD) Set(key string, values ...string) {
+func (m *MD) Set(key string, values ...string) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
 	key = strings.ToLower(key)
 	if len(values) == 0 {
-		delete(m, key)
+		delete(m.data, key)
 		return
 	}
-	m[key] = values
+	m.data[key] = values
 }
 
 // Append appends additional values to the given key.
-func (m MD) Append(key string, values ...string) {
+func (m *MD) Append(key string, values ...string) {
 	key = strings.ToLower(key)
 	if len(values) == 0 {
 		return
 	}
-	current, ok := m[key]
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	current, ok := m.data[key]
 	if ok {
-		m.Set(key, append(current, values...)...)
+		m.data[key] = append(current, values...)
 	} else {
-		m.Set(key, values...)
+		m.data[key] = values
 	}
 }
 
-func (m MD) setRequest(r *Request) {
-	for k, values := range m {
+// GetCopy returns the metadata for a given key when they exist.
+func (m *MD) GetCopy() map[string][]string {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	mCopy := make(map[string][]string, len(m.data))
+	for key, value := range m.data {
+		mCopy[key] = value
+	}
+
+	return mCopy
+}
+
+func (m *MD) setRequest(r *Request) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	for k, values := range m.data {
 		for _, v := range values {
 			r.Metadata = append(r.Metadata, &KeyValue{
 				Key:   k,
@@ -73,17 +110,20 @@ func (m MD) setRequest(r *Request) {
 	}
 }
 
-func (m MD) fromRequest(r *Request) {
+func (m *MD) fromRequest(r *Request) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
 	for _, kv := range r.Metadata {
-		m[kv.Key] = append(m[kv.Key], kv.Value)
+		m.data[kv.Key] = append(m.data[kv.Key], kv.Value)
 	}
 }
 
 type metadataKey struct{}
 
 // GetMetadata retrieves metadata from context.Context (previously attached with WithMetadata)
-func GetMetadata(ctx context.Context) (MD, bool) {
-	metadata, ok := ctx.Value(metadataKey{}).(MD)
+func GetMetadata(ctx context.Context) (*MD, bool) {
+	metadata, ok := ctx.Value(metadataKey{}).(*MD)
 	return metadata, ok
 }
 
@@ -102,6 +142,6 @@ func GetMetadataValue(ctx context.Context, name string) (string, bool) {
 }
 
 // WithMetadata attaches metadata map to a context.Context
-func WithMetadata(ctx context.Context, md MD) context.Context {
+func WithMetadata(ctx context.Context, md *MD) context.Context {
 	return context.WithValue(ctx, metadataKey{}, md)
 }
diff --git a/metadata_test.go b/metadata_test.go
index d7fc09559..d1e932cdf 100644
--- a/metadata_test.go
+++ b/metadata_test.go
@@ -22,7 +22,7 @@ import (
 )
 
 func TestMetadataGet(t *testing.T) {
-	metadata := make(MD)
+	metadata := NewMD(make(map[string][]string))
 	metadata.Set("foo", "1", "2")
 
 	if list, ok := metadata.Get("foo"); !ok {
@@ -37,7 +37,7 @@ func TestMetadataGet(t *testing.T) {
 }
 
 func TestMetadataGetInvalidKey(t *testing.T) {
-	metadata := make(MD)
+	metadata := NewMD(make(map[string][]string))
 	metadata.Set("foo", "1", "2")
 
 	if _, ok := metadata.Get("invalid"); ok {
@@ -46,7 +46,7 @@ func TestMetadataGetInvalidKey(t *testing.T) {
 }
 
 func TestMetadataUnset(t *testing.T) {
-	metadata := make(MD)
+	metadata := NewMD(make(map[string][]string))
 	metadata.Set("foo", "1", "2")
 	metadata.Set("foo")
 
@@ -56,7 +56,7 @@ func TestMetadataUnset(t *testing.T) {
 }
 
 func TestMetadataReplace(t *testing.T) {
-	metadata := make(MD)
+	metadata := NewMD(make(map[string][]string))
 	metadata.Set("foo", "1", "2")
 	metadata.Set("foo", "3", "4")
 
@@ -72,7 +72,7 @@ func TestMetadataReplace(t *testing.T) {
 }
 
 func TestMetadataAppend(t *testing.T) {
-	metadata := make(MD)
+	metadata := NewMD(make(map[string][]string))
 	metadata.Set("foo", "1")
 	metadata.Append("foo", "2")
 	metadata.Append("bar", "3")
@@ -95,7 +95,7 @@ func TestMetadataAppend(t *testing.T) {
 }
 
 func TestMetadataContext(t *testing.T) {
-	metadata := make(MD)
+	metadata := NewMD(make(map[string][]string))
 	metadata.Set("foo", "bar")
 
 	ctx := WithMetadata(context.Background(), metadata)
diff --git a/server.go b/server.go
index bb71de677..50b0f34c4 100644
--- a/server.go
+++ b/server.go
@@ -571,7 +571,7 @@ var noopFunc = func() {}
 
 func getRequestContext(ctx context.Context, req *Request) (retCtx context.Context, cancel func()) {
 	if len(req.Metadata) > 0 {
-		md := MD{}
+		md := NewMD(make(map[string][]string))
 		md.fromRequest(req)
 		ctx = WithMetadata(ctx, md)
 	}
diff --git a/server_test.go b/server_test.go
index 4a1561df8..537418125 100644
--- a/server_test.go
+++ b/server_test.go
@@ -550,7 +550,7 @@ func roundTrip(ctx context.Context, client *testingClient, name string) callResu
 		}
 	)
 
-	ctx = WithMetadata(ctx, MD{"foo": []string{name}})
+	ctx = WithMetadata(ctx, NewMD(map[string][]string{"foo": {name}}))
 
 	resp, err := client.Test(ctx, tp)
 	if err != nil {