diff --git a/bot.go b/bot.go
index d44ae54..2fc190c 100644
--- a/bot.go
+++ b/bot.go
@@ -198,18 +198,7 @@ func (bot *BotAPI) UploadFiles(endpoint string, params Params, files []RequestFi
 					return
 				}
 
-				if f.Size != -1 {
-					io.Copy(part, f.Reader)
-				} else {
-					data, err := ioutil.ReadAll(f.Reader)
-					if err != nil {
-						w.CloseWithError(err)
-						return
-					}
-
-					buf := bytes.NewBuffer(data)
-					io.Copy(part, buf)
-				}
+				io.Copy(part, f.Reader)
 			case FileURL:
 				val := string(f)
 				if err := m.WriteField(file.Name, val); err != nil {
diff --git a/bot_test.go b/bot_test.go
index 9645efa..537dcc3 100644
--- a/bot_test.go
+++ b/bot_test.go
@@ -120,7 +120,7 @@ func TestSendWithNewPhotoWithFileReader(t *testing.T) {
 	bot, _ := getBot(t)
 
 	f, _ := os.Open("tests/image.jpg")
-	reader := FileReader{Name: "image.jpg", Reader: f, Size: -1}
+	reader := FileReader{Name: "image.jpg", Reader: f}
 
 	msg := NewPhoto(ChatID, reader)
 	msg.Caption = "Test"
@@ -177,7 +177,7 @@ func TestSendNewPhotoToChannelFileReader(t *testing.T) {
 	bot, _ := getBot(t)
 
 	f, _ := os.Open("tests/image.jpg")
-	reader := FileReader{Name: "image.jpg", Reader: f, Size: -1}
+	reader := FileReader{Name: "image.jpg", Reader: f}
 
 	msg := NewPhotoToChannel(Channel, reader)
 	msg.Caption = "Test"
diff --git a/configs.go b/configs.go
index 2b15c16..925766f 100644
--- a/configs.go
+++ b/configs.go
@@ -375,10 +375,6 @@ func (config AnimationConfig) params() (Params, error) {
 	return params, err
 }
 
-func (config AnimationConfig) name() string {
-	return "animation"
-}
-
 func (config AnimationConfig) method() string {
 	return "sendAnimation"
 }
@@ -899,8 +895,15 @@ func (config WebhookConfig) params() (Params, error) {
 	return params, err
 }
 
-func (config WebhookConfig) name() string {
-	return "certificate"
+func (config WebhookConfig) files() []RequestFile {
+	if config.Certificate != nil {
+		return []RequestFile{{
+			Name: "certificate",
+			File: config.Certificate,
+		}}
+	}
+
+	return nil
 }
 
 // RemoveWebhookConfig is a helper to remove a webhook.
@@ -923,12 +926,9 @@ type FileBytes struct {
 }
 
 // FileReader contains information about a reader to upload as a File.
-// If Size is -1, it will read the entire Reader into memory to
-// calculate a Size.
 type FileReader struct {
 	Name   string
 	Reader io.Reader
-	Size   int64
 }
 
 // FileURL is a URL to use as a file for a request.
@@ -1642,15 +1642,14 @@ func (config SetStickerSetThumbConfig) params() (Params, error) {
 	params["name"] = config.Name
 	params.AddNonZero("user_id", config.UserID)
 
-	if thumb, ok := config.Thumb.(string); ok {
-		params["thumb"] = thumb
-	}
-
 	return params, nil
 }
 
-func (config SetStickerSetThumbConfig) name() string {
-	return "thumb"
+func (config SetStickerSetThumbConfig) files() []RequestFile {
+	return []RequestFile{{
+		Name: "thumb",
+		File: config.Thumb,
+	}}
 }
 
 // SetChatStickerSetConfig allows you to set the sticker set for a supergroup.
diff --git a/types_test.go b/types_test.go
index 3b6c5be..354625c 100644
--- a/types_test.go
+++ b/types_test.go
@@ -349,4 +349,6 @@ var (
 	_ Fileable = (*NewStickerSetConfig)(nil)
 	_ Fileable = (*AddStickerConfig)(nil)
 	_ Fileable = (*MediaGroupConfig)(nil)
+	_ Fileable = (*WebhookConfig)(nil)
+	_ Fileable = (*SetStickerSetThumbConfig)(nil)
 )