diff --git a/td/telegram/MessageViewer.h b/td/telegram/MessageViewer.h
index 4df57c341..6ea77c121 100644
--- a/td/telegram/MessageViewer.h
+++ b/td/telegram/MessageViewer.h
@@ -48,9 +48,12 @@ bool operator!=(const MessageViewer &lhs, const MessageViewer &rhs);
 
 StringBuilder &operator<<(StringBuilder &string_builder, const MessageViewer &viewer);
 
-struct MessageViewers {
+class MessageViewers {
   vector<MessageViewer> message_viewers_;
 
+  friend StringBuilder &operator<<(StringBuilder &string_builder, const MessageViewers &viewers);
+
+ public:
   MessageViewers() = default;
 
   explicit MessageViewers(vector<telegram_api::object_ptr<telegram_api::storyView>> &&story_views);
diff --git a/td/telegram/MessagesManager.cpp b/td/telegram/MessagesManager.cpp
index f4ec32308..85f355150 100644
--- a/td/telegram/MessagesManager.cpp
+++ b/td/telegram/MessagesManager.cpp
@@ -18200,8 +18200,7 @@ void MessagesManager::on_get_message_viewers(DialogId dialog_id, MessageViewers
                                              Promise<td_api::object_ptr<td_api::messageViewers>> &&promise) {
   if (!is_recursive) {
     bool need_participant_list = false;
-    for (auto message_viewer : message_viewers.message_viewers_) {
-      auto user_id = message_viewer.get_user_id();
+    for (auto user_id : message_viewers.get_user_ids()) {
       if (!user_id.is_valid()) {
         LOG(ERROR) << "Receive invalid " << user_id << " as viewer of a message in " << dialog_id;
         continue;