diff --git a/td/telegram/MessagesManager.cpp b/td/telegram/MessagesManager.cpp
index 89d6f41b..3b3fe13e 100644
--- a/td/telegram/MessagesManager.cpp
+++ b/td/telegram/MessagesManager.cpp
@@ -3602,6 +3602,96 @@ class MessagesManager::UploadDialogPhotoCallback : public FileManager::UploadCal
   }
 };
 
+StringBuilder &operator<<(StringBuilder &string_builder, MessageContentType content_type) {
+  switch (content_type) {
+    case MessageContentType::None:
+      return string_builder << "None";
+    case MessageContentType::Animation:
+      return string_builder << "Animation";
+    case MessageContentType::Audio:
+      return string_builder << "Audio";
+    case MessageContentType::Document:
+      return string_builder << "Document";
+    case MessageContentType::ExpiredPhoto:
+      return string_builder << "ExpiredPhoto";
+    case MessageContentType::Photo:
+      return string_builder << "Photo";
+    case MessageContentType::ExpiredVideo:
+      return string_builder << "ExpiredVideo";
+    case MessageContentType::Video:
+      return string_builder << "Video";
+    case MessageContentType::VideoNote:
+      return string_builder << "VideoNote";
+    case MessageContentType::VoiceNote:
+      return string_builder << "VoiceNote";
+    case MessageContentType::Contact:
+      return string_builder << "Contact";
+    case MessageContentType::LiveLocation:
+      return string_builder << "LiveLocation";
+    case MessageContentType::Location:
+      return string_builder << "Location";
+    case MessageContentType::Venue:
+      return string_builder << "Venue";
+    case MessageContentType::Game:
+      return string_builder << "Game";
+    case MessageContentType::Invoice:
+      return string_builder << "Invoice";
+    case MessageContentType::Sticker:
+      return string_builder << "Sticker";
+    case MessageContentType::Text:
+      return string_builder << "Text";
+    case MessageContentType::Unsupported:
+      return string_builder << "Unsupported";
+    case MessageContentType::ChatCreate:
+      return string_builder << "ChatCreate";
+    case MessageContentType::ChatChangeTitle:
+      return string_builder << "ChatChangeTitle";
+    case MessageContentType::ChatChangePhoto:
+      return string_builder << "ChatChangePhoto";
+    case MessageContentType::ChatDeletePhoto:
+      return string_builder << "ChatDeletePhoto";
+    case MessageContentType::ChatDeleteHistory:
+      return string_builder << "ChatDeleteHistory";
+    case MessageContentType::ChatAddUsers:
+      return string_builder << "ChatAddUsers";
+    case MessageContentType::ChatJoinedByLink:
+      return string_builder << "ChatJoinedByLink";
+    case MessageContentType::ChatDeleteUser:
+      return string_builder << "ChatDeleteUser";
+    case MessageContentType::ChatMigrateTo:
+      return string_builder << "ChatMigrateTo";
+    case MessageContentType::ChannelCreate:
+      return string_builder << "ChannelCreate";
+    case MessageContentType::ChannelMigrateFrom:
+      return string_builder << "ChannelMigrateFrom";
+    case MessageContentType::PinMessage:
+      return string_builder << "PinMessage";
+    case MessageContentType::GameScore:
+      return string_builder << "GameScore";
+    case MessageContentType::ScreenshotTaken:
+      return string_builder << "ScreenshotTaken";
+    case MessageContentType::ChatSetTtl:
+      return string_builder << "ChatSetTtl";
+    case MessageContentType::Call:
+      return string_builder << "Call";
+    case MessageContentType::PaymentSuccessful:
+      return string_builder << "PaymentSuccessful";
+    case MessageContentType::ContactRegistered:
+      return string_builder << "ContactRegistered";
+    case MessageContentType::CustomServiceAction:
+      return string_builder << "CustomServiceAction";
+    case MessageContentType::WebsiteConnected:
+      return string_builder << "WebsiteConnected";
+    case MessageContentType::PassportDataSent:
+      return string_builder << "PassportDataSent";
+    case MessageContentType::PassportDataReceived:
+      return string_builder << "PassportDataReceived";
+    default:
+      UNREACHABLE();
+      return string_builder;
+  }
+}
+
 template <class StorerT>
 static void store(const MessageContent *content, StorerT &storer) {
   CHECK(content != nullptr);
diff --git a/td/telegram/MessagesManager.h b/td/telegram/MessagesManager.h
index 88300578..faa747e4 100644
--- a/td/telegram/MessagesManager.h
+++ b/td/telegram/MessagesManager.h
@@ -113,10 +113,7 @@ enum class MessageContentType : int32 {
   PassportDataReceived
 };
 
-inline StringBuilder &operator<<(StringBuilder &string_builder, MessageContentType content_type) {
-  // TODO
-  return string_builder << static_cast<int32>(content_type);
-}
+StringBuilder &operator<<(StringBuilder &string_builder, MessageContentType content_type);
 
 // Do not forget to update MessagesManager::update_message_content when one of the inheritors of this class changes
 class MessageContent {