diff --git a/CHANGELOG.md b/CHANGELOG.md
index 854d9ca..0605053 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ Please check the [Upgrading Instructions](UPGRADE.md) when upgrading to a newer
 ### Removed
 
 ### Fixed
+- #13 Oauth authorization and access token responses set correct `Content-Type: application/json; charset=UTF-8` headers (raimon-segura, rhertogh)
 - #14 Migrations now handle `tinyint`, `smallint` and `bigint` data types for `user` table primary key correctly (mtangoo, rhertogh) 
 
 ### Improved
diff --git a/src/controllers/web/server/Oauth2AccessTokenAction.php b/src/controllers/web/server/Oauth2AccessTokenAction.php
index b901a9a..4114213 100644
--- a/src/controllers/web/server/Oauth2AccessTokenAction.php
+++ b/src/controllers/web/server/Oauth2AccessTokenAction.php
@@ -8,6 +8,7 @@
 use rhertogh\Yii2Oauth2Server\helpers\Psr7Helper;
 use Yii;
 use yii\web\HttpException;
+use yii\web\Response;
 
 /**
  * @property Oauth2ServerController $controller
@@ -24,7 +25,9 @@ public function run()
             $psr7Request = Psr7Helper::yiiToPsr7Request(Yii::$app->request);
             $psr7Response = Psr7Helper::yiiToPsr7Response(Yii::$app->response);
             $psr7Response = $server->respondToAccessTokenRequest($psr7Request, $psr7Response);
-            return Psr7Helper::psr7ToYiiResponse($psr7Response);
+            return Psr7Helper::psr7ToYiiResponse($psr7Response, [
+                'format' => Response::FORMAT_JSON,
+            ]);
         } catch (\Exception $e) {
             Yii::error((string)$e, __METHOD__);
             return $this->processException($e);
diff --git a/src/controllers/web/server/Oauth2AuthorizeAction.php b/src/controllers/web/server/Oauth2AuthorizeAction.php
index f508a47..fcd405b 100644
--- a/src/controllers/web/server/Oauth2AuthorizeAction.php
+++ b/src/controllers/web/server/Oauth2AuthorizeAction.php
@@ -20,6 +20,7 @@
 use yii\web\BadRequestHttpException;
 use yii\web\HttpException;
 use yii\web\Request;
+use yii\web\Response;
 use yii\web\UnauthorizedHttpException;
 
 /**
@@ -334,7 +335,9 @@ public function run($clientAuthorizationRequestId = null)
             $psr7Response = Psr7Helper::yiiToPsr7Response(Yii::$app->response);
             $psr7Response = $server->completeAuthorizationRequest($authRequest, $psr7Response);
 
-            return Psr7Helper::psr7ToYiiResponse($psr7Response);
+            return Psr7Helper::psr7ToYiiResponse($psr7Response, [
+                'format' => Response::FORMAT_JSON,
+            ]);
         } catch (\Exception $e) {
             Yii::error((string)$e, __METHOD__);
             return $this->processException($e);
diff --git a/src/helpers/Psr7Helper.php b/src/helpers/Psr7Helper.php
index 801b068..3dd54ae 100644
--- a/src/helpers/Psr7Helper.php
+++ b/src/helpers/Psr7Helper.php
@@ -7,6 +7,7 @@
 use GuzzleHttp\Psr7\Utils as Psr7Utils;
 use Psr\Http\Message\ServerRequestInterface;
 use Yii;
+use yii\helpers\ArrayHelper;
 use yii\web\Request;
 use yii\web\Response;
 
@@ -58,14 +59,17 @@ public static function yiiToPsr7Response($response)
      * @return Response
      * @since 1.0.0
      */
-    public static function psr7ToYiiResponse($psr7Response)
+    public static function psr7ToYiiResponse($psr7Response, $defaultConfig = [])
     {
         /** @var Response $response */
-        $response = Yii::createObject([
-            'class' => Response::class,
-            'statusCode' => $psr7Response->getStatusCode(),
-            'content' => (string)$psr7Response->getBody(),
-        ]);
+        $response = Yii::createObject(ArrayHelper::merge(
+            [
+                'class' => Response::class,
+                'statusCode' => $psr7Response->getStatusCode(),
+                'content' => (string)$psr7Response->getBody(),
+            ],
+            $defaultConfig,
+        ));
 
         $response->headers->fromArray(array_change_key_case($psr7Response->getHeaders(), CASE_LOWER));