diff --git a/oauth2.go b/oauth2.go
index 62f1a6a9..31cae9ad 100644
--- a/oauth2.go
+++ b/oauth2.go
@@ -33,7 +33,7 @@ type tokenRespBody struct {
 type TokenFetcher interface {
 	// FetchToken retrieves a new access token for the provider.
 	// If the implementation doesn't know how to retrieve a new token,
-	// it returns an error.
+	// it returns an error. Existing token could be nil.
 	FetchToken(existing *Token) (*Token, error)
 }
 
@@ -173,12 +173,11 @@ func (c *Config) FetchToken(existing *Token) (*Token, error) {
 	if existing == nil || existing.RefreshToken == "" {
 		return nil, errors.New("cannot fetch access token without refresh token.")
 	}
-	err := c.updateToken(existing, url.Values{
+	return c.retrieveToken(url.Values{
 		"grant_type":    {"refresh_token"},
 		"client_secret": {c.opts.ClientSecret},
 		"refresh_token": {existing.RefreshToken},
 	})
-	return existing, err
 }
 
 // Checks if all required configuration fields have non-zero values.
@@ -195,7 +194,6 @@ func (c *Config) validate() error {
 // Exchange exchanges the exchange code with the OAuth 2.0 provider
 // to retrieve a new access token.
 func (c *Config) Exchange(exchangeCode string) (*Token, error) {
-	token := &Token{}
 	vals := url.Values{
 		"grant_type":    {"authorization_code"},
 		"client_secret": {c.opts.ClientSecret},
@@ -207,15 +205,10 @@ func (c *Config) Exchange(exchangeCode string) (*Token, error) {
 	if c.opts.RedirectURL != "" {
 		vals.Set("redirect_uri", c.opts.RedirectURL)
 	}
-	err := c.updateToken(token, vals)
-	if err != nil {
-		return nil, err
-	}
-	return token, nil
+	return c.retrieveToken(vals)
 }
 
-// updateToken mutates both tok and v.
-func (c *Config) updateToken(tok *Token, v url.Values) error {
+func (c *Config) retrieveToken(v url.Values) (*Token, error) {
 	v.Set("client_id", c.opts.ClientID)
 	// Note that we're not setting v's client_secret to t.ClientSecret, due
 	// to https://code.google.com/p/goauth2/issues/detail?id=31
@@ -225,12 +218,12 @@ func (c *Config) updateToken(tok *Token, v url.Values) error {
 	// so that's all we use.
 	r, err := http.DefaultClient.PostForm(c.tokenURL.String(), v)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	defer r.Body.Close()
 	if r.StatusCode != 200 {
 		// TODO(jbd): Add status code or error message
-		return errors.New("Error during updating token.")
+		return nil, errors.New("error during updating token")
 	}
 
 	resp := &tokenRespBody{}
@@ -239,11 +232,11 @@ func (c *Config) updateToken(tok *Token, v url.Values) error {
 	case "application/x-www-form-urlencoded", "text/plain":
 		body, err := ioutil.ReadAll(r.Body)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		vals, err := url.ParseQuery(string(body))
 		if err != nil {
-			return err
+			return nil, err
 		}
 		resp.AccessToken = vals.Get("access_token")
 		resp.TokenType = vals.Get("token_type")
@@ -252,25 +245,29 @@ func (c *Config) updateToken(tok *Token, v url.Values) error {
 		resp.IdToken = vals.Get("id_token")
 	default:
 		if err = json.NewDecoder(r.Body).Decode(&resp); err != nil {
-			return err
+			return nil, err
 		}
 	}
-	tok.AccessToken = resp.AccessToken
-	tok.TokenType = resp.TokenType
+	token := &Token{
+		AccessToken:  resp.AccessToken,
+		TokenType:    resp.TokenType,
+		RefreshToken: resp.RefreshToken,
+	}
 	// Don't overwrite `RefreshToken` with an empty value
-	if resp.RefreshToken != "" {
-		tok.RefreshToken = resp.RefreshToken
+	// if this was a token refreshing request.
+	if resp.RefreshToken == "" {
+		token.RefreshToken = v.Get("refresh_token")
 	}
 	if resp.ExpiresIn == 0 {
-		tok.Expiry = time.Time{}
+		token.Expiry = time.Time{}
 	} else {
-		tok.Expiry = time.Now().Add(time.Duration(resp.ExpiresIn) * time.Second)
+		token.Expiry = time.Now().Add(time.Duration(resp.ExpiresIn) * time.Second)
 	}
 	if resp.IdToken != "" {
-		if tok.Extra == nil {
-			tok.Extra = make(map[string]string)
+		if token.Extra == nil {
+			token.Extra = make(map[string]string)
 		}
-		tok.Extra["id_token"] = resp.IdToken
+		token.Extra["id_token"] = resp.IdToken
 	}
-	return nil
+	return token, nil
 }