diff --git a/lib/src/http_util.dart b/lib/src/http_util.dart
index 566b305..f712198 100644
--- a/lib/src/http_util.dart
+++ b/lib/src/http_util.dart
@@ -38,7 +38,8 @@ dynamic _processResponse(http.Response response) {
       .value;
   var isJson = contentType.split(';').first == 'application/json';
 
-  var body = isJson ? json.decode(response.body) : response.body;
+  var body = isJson ? json.decode(utf8.decode(response.body)) : response.body;
+
   if (body is Map && body['error'] is String) {
     throw OpenIdException(
         body['error'], body['error_description'], body['error_uri']);