diff --git a/form.go b/form.go
index 5dc1ca7..2aad714 100644
--- a/form.go
+++ b/form.go
@@ -25,45 +25,55 @@ const (
 	ContentTypeXML           = "application/xml"
 )
 
-var decoders = make(map[string]Decoder)
+var defaultDecoders = &Decoders{}
 
 var defaultDecoder = schema.NewDecoder()
 var defaultMaxMemory int64 = 10 * 1024 * 1024
 
-func init() {
-}
-
 func init() {
 	defaultDecoder.IgnoreUnknownKeys(true)
 	defaultDecoder.SetAliasTag("json")
 
-	Register(ContentTypeForm, NewForm(defaultDecoder))
-	Register(ContentTypeMultipartForm, NewMultipartForm(defaultMaxMemory))
-	Register(ContentTypeJSON, JSON)
-	Register(ContentTypeXML, XML)
+	defaultDecoders.Register(ContentTypeForm, NewForm(defaultDecoder))
+	defaultDecoders.Register(ContentTypeMultipartForm, NewMultipartForm(defaultMaxMemory))
+	defaultDecoders.Register(ContentTypeJSON, JSON)
+	defaultDecoders.Register(ContentTypeXML, XML)
 }
 
 // Register a decoder for the given content type.
 func Register(contentType string, decoder Decoder) {
-	decoders[contentType] = decoder
+	defaultDecoders.Register(contentType, decoder)
 }
 
-// Decoder is a function that decode data from request into v.
-type Decoder func(req *http.Request, v interface{}) error
-
 // Decode data from a request into v, v should be a pointer.
 func Decode(r *http.Request, v interface{}) error {
+	return defaultDecoders.Decode(r, v)
+}
+
+// Decoders is a map that mapping from content type to decoder.
+type Decoders map[string]Decoder
+
+// Register a decoder for the given content type.
+func (d *Decoders) Register(contentType string, decoder Decoder) {
+	(*d)[contentType] = decoder
+}
+
+// Decode data from a request into v, v should be a pointer.
+func (d *Decoders) Decode(r *http.Request, v interface{}) error {
 	contentType, err := parseContentType(r)
 	if err != nil {
 		return err
 	}
-	if decoder, ok := decoders[contentType]; ok {
+	if decoder, ok := (*d)[contentType]; ok {
 		return decoder(r, v)
 	}
 
 	return errors.New("Unsupported content type: " + contentType)
 }
 
+// Decoder is a function that decode data from request into v.
+type Decoder func(req *http.Request, v interface{}) error
+
 func parseContentType(r *http.Request) (string, error) {
 	header := r.Header.Get(ContentType)
 	contentType, _, err := mime.ParseMediaType(header)
diff --git a/form_test.go b/form_test.go
index ff9daa5..6f0a014 100644
--- a/form_test.go
+++ b/form_test.go
@@ -28,7 +28,7 @@ func TestRegister(t *testing.T) {
 	}
 	contentType := "content/type"
 	Register(contentType, decoder)
-	actual, ok := decoders[contentType]
+	actual, ok := (*defaultDecoders)[contentType]
 	if !ok {
 		t.Error("Failed to register decoder")
 	}
@@ -200,7 +200,7 @@ func TestParseContentType(t *testing.T) {
 }
 
 func TestDecode(t *testing.T) {
-	delete(decoders, "application/json")
+	delete((*defaultDecoders), "application/json")
 	req := httptest.NewRequest(http.MethodPost, "/login", nil)
 	req.Header.Set("Content-Type", "application/json")
 	v := login{}