diff --git a/auth.go b/auth.go
index 2788b634..678741df 100644
--- a/auth.go
+++ b/auth.go
@@ -73,7 +73,9 @@ func (c *fileTokenSource) Token() (*oauth2.Token, error) {
 	}
 
 	var tk *oauth2.Token
-	if c.style == authStyleNotKnown || c.style == authStyleInHeader {
+
+	switch {
+	case c.style == authStyleNotKnown, c.style == authStyleInHeader:
 		tk, err = retrieveToken(c.ctx, c.conf.TokenURL, c.conf.ClientID, string(content), v, authStyleInHeader)
 		if err == nil {
 			c.style = authStyleInHeader
@@ -86,7 +88,7 @@ func (c *fileTokenSource) Token() (*oauth2.Token, error) {
 				return tk, nil
 			}
 		}
-	} else if c.style == authStyleInParams {
+	case c.style == authStyleInParams:
 		tk, err = retrieveToken(c.ctx, c.conf.TokenURL, c.conf.ClientID, string(content), v, authStyleInParams)
 		if err == nil {
 			c.style = authStyleInParams
@@ -108,7 +110,7 @@ func buildHeadersAndBody(clientID, clientSecret string, v url.Values, style auth
 		"Content-Type": "application/x-www-form-urlencoded",
 	}
 	switch style {
-	case authStyleInHeader:
+	case authStyleInHeader, authStyleNotKnown:
 		headers["Authorization"] = "Basic " + BasicAuth(url.QueryEscape(clientID), url.QueryEscape(clientSecret))
 	case authStyleInParams:
 		v.Set("client_id", clientID)