diff --git a/td/telegram/MessagesManager.cpp b/td/telegram/MessagesManager.cpp
index d07de297f..150995aa3 100644
--- a/td/telegram/MessagesManager.cpp
+++ b/td/telegram/MessagesManager.cpp
@@ -16087,7 +16087,9 @@ void MessagesManager::add_random_id_to_message_id_correspondence(Dialog *d, int6
   auto it = d->random_id_to_message_id.find(random_id);
   if (it == d->random_id_to_message_id.end() || it->second.get() < message_id.get()) {
     LOG(INFO) << "Add correspondence from random_id " << random_id << " to " << message_id << " in " << d->dialog_id;
-    d->random_id_to_message_id[random_id] = message_id;
+    if (random_id != 0) {
+      d->random_id_to_message_id[random_id] = message_id;
+    }
   }
 }
 
@@ -36390,7 +36392,7 @@ MessageId MessagesManager::get_message_id_by_random_id(Dialog *d, int64 random_i
   }
   auto it = d->random_id_to_message_id.find(random_id);
   if (it == d->random_id_to_message_id.end()) {
-    if (G()->use_message_database() && d->dialog_id.get_type() == DialogType::SecretChat) {
+    if (G()->use_message_database() && d->dialog_id.get_type() == DialogType::SecretChat && random_id != 0) {
       auto r_value = G()->td_db()->get_message_db_sync()->get_message_by_random_id(d->dialog_id, random_id);
       if (r_value.is_ok()) {
         debug_add_message_to_dialog_fail_reason_ = "not called";
diff --git a/td/telegram/MessagesManager.h b/td/telegram/MessagesManager.h
index edb681cc9..a9174e801 100644
--- a/td/telegram/MessagesManager.h
+++ b/td/telegram/MessagesManager.h
@@ -1453,8 +1453,7 @@ class MessagesManager final : public Actor {
     int32 pending_read_channel_inbox_pts = 0;                  // for channels only
     int32 pending_read_channel_inbox_server_unread_count = 0;  // for channels only
     MessageId pending_read_channel_inbox_max_message_id;       // for channels only
-    std::unordered_map<int64, MessageId, Hash<int64>>
-        random_id_to_message_id;  // for secret chats and yet unsent messages only
+    FlatHashMap<int64, MessageId> random_id_to_message_id;     // for secret chats and yet unsent messages only
 
     MessageId last_assigned_message_id;  // identifier of the last local or yet unsent message, assigned after
                                          // application start, used to guarantee that all assigned message identifiers