diff --git a/src/League/OAuth2/Server/Grant/RefreshToken.php b/src/League/OAuth2/Server/Grant/RefreshToken.php
index baea674a..baf890f3 100644
--- a/src/League/OAuth2/Server/Grant/RefreshToken.php
+++ b/src/League/OAuth2/Server/Grant/RefreshToken.php
@@ -192,7 +192,7 @@ class RefreshToken implements GrantTypeInterface {
 
         $response = array(
             'access_token'  =>  $accessToken,
-            'token_type'    =>  'bearer',
+            'token_type'    =>  'Bearer',
             'expires'       =>  $accessTokenExpires,
             'expires_in'    =>  $accessTokenExpiresIn
         );