diff --git a/benchmark/bench_misc.cpp b/benchmark/bench_misc.cpp
index e3671a3e7..aeec2232a 100644
--- a/benchmark/bench_misc.cpp
+++ b/benchmark/bench_misc.cpp
@@ -533,40 +533,40 @@ class MessageIdDuplicateCheckerNewSimple {
   std::set<td::int64> saved_message_ids_;
 };
 
-template <size_t MAX_SAVED_MESSAGE_IDS>
+template <size_t max_size>
 class MessageIdDuplicateCheckerArray {
  public:
   static td::string get_description() {
-    return PSTRING() << "Array" << MAX_SAVED_MESSAGE_IDS;
+    return PSTRING() << "Array" << max_size;
   }
   td::Status check(td::int64 message_id) {
-    if (end_pos == 2 * MAX_SAVED_MESSAGE_IDS) {
-      std::copy_n(&saved_message_ids_[MAX_SAVED_MESSAGE_IDS], MAX_SAVED_MESSAGE_IDS, &saved_message_ids_[0]);
-      end_pos = MAX_SAVED_MESSAGE_IDS;
+    if (end_pos_ == 2 * max_size) {
+      std::copy_n(&saved_message_ids_[max_size], max_size, &saved_message_ids_[0]);
+      end_pos_ = max_size;
     }
-    if (end_pos == 0 || message_id > saved_message_ids_[end_pos - 1]) {
+    if (end_pos_ == 0 || message_id > saved_message_ids_[end_pos_ - 1]) {
       // fast path
-      saved_message_ids_[end_pos++] = message_id;
+      saved_message_ids_[end_pos_++] = message_id;
       return td::Status::OK();
     }
-    if (end_pos >= MAX_SAVED_MESSAGE_IDS && message_id < saved_message_ids_[0]) {
+    if (end_pos_ >= max_size && message_id < saved_message_ids_[0]) {
       return td::Status::Error(2, PSLICE() << "Ignore very old message_id "
                                            << td::tag("oldest message_id", saved_message_ids_[0])
                                            << td::tag("got message_id", message_id));
     }
-    auto it = std::lower_bound(&saved_message_ids_[0], &saved_message_ids_[end_pos], message_id);
+    auto it = std::lower_bound(&saved_message_ids_[0], &saved_message_ids_[end_pos_], message_id);
     if (*it == message_id) {
       return td::Status::Error(1, PSLICE() << "Ignore duplicated message_id " << td::tag("message_id", message_id));
     }
-    std::copy_backward(it, &saved_message_ids_[end_pos], &saved_message_ids_[end_pos + 1]);
+    std::copy_backward(it, &saved_message_ids_[end_pos_], &saved_message_ids_[end_pos_ + 1]);
     *it = message_id;
-    ++end_pos;
+    ++end_pos_;
     return td::Status::OK();
   }
 
  private:
-  std::array<td::int64, 2 * MAX_SAVED_MESSAGE_IDS> saved_message_ids_;
-  std::size_t end_pos = 0;
+  std::array<td::int64, 2 * max_size> saved_message_ids_;
+  std::size_t end_pos_ = 0;
 };
 
 template <class T>
diff --git a/td/mtproto/AuthData.cpp b/td/mtproto/AuthData.cpp
index 189c74cd1..2dfff4bcd 100644
--- a/td/mtproto/AuthData.cpp
+++ b/td/mtproto/AuthData.cpp
@@ -17,25 +17,31 @@
 namespace td {
 namespace mtproto {
 
-Status MessageIdDuplicateChecker::check(int64 message_id) {
+Status check_message_id_duplicates(int64 *saved_message_ids, size_t max_size, size_t &end_pos, int64 message_id) {
   // In addition, the identifiers (msg_id) of the last N messages received from the other side must be stored, and if
   // a message comes in with msg_id lower than all or equal to any of the stored values, that message is to be
   // ignored. Otherwise, the new message msg_id is added to the set, and, if the number of stored msg_id values is
   // greater than N, the oldest (i. e. the lowest) is forgotten.
-  auto insert_result = saved_message_ids_.insert(message_id);
-  if (!insert_result.second) {
+  if (end_pos == 2 * max_size) {
+    std::copy_n(&saved_message_ids[max_size], max_size, &saved_message_ids[0]);
+    end_pos = max_size;
+  }
+  if (end_pos == 0 || message_id > saved_message_ids[end_pos - 1]) {
+    // fast path
+    saved_message_ids[end_pos++] = message_id;
+    return Status::OK();
+  }
+  if (end_pos >= max_size && message_id < saved_message_ids[0]) {
+    return Status::Error(2, PSLICE() << "Ignore very old message_id " << tag("oldest message_id", saved_message_ids[0])
+                                     << tag("got message_id", message_id));
+  }
+  auto it = std::lower_bound(&saved_message_ids[0], &saved_message_ids[end_pos], message_id);
+  if (*it == message_id) {
     return Status::Error(1, PSLICE() << "Ignore duplicated message_id " << tag("message_id", message_id));
   }
-  if (saved_message_ids_.size() == MAX_SAVED_MESSAGE_IDS + 1) {
-    auto begin_it = saved_message_ids_.begin();
-    bool is_very_old = begin_it == insert_result.first;
-    saved_message_ids_.erase(begin_it);
-    if (is_very_old) {
-      return Status::Error(2, PSLICE() << "Ignore very old message_id "
-                                       << tag("oldest message_id", *saved_message_ids_.begin())
-                                       << tag("got message_id", message_id));
-    }
-  }
+  std::copy_backward(it, &saved_message_ids[end_pos], &saved_message_ids[end_pos + 1]);
+  *it = message_id;
+  ++end_pos;
   return Status::OK();
 }
 
diff --git a/td/mtproto/AuthData.h b/td/mtproto/AuthData.h
index 4a9717048..89d34f02b 100644
--- a/td/mtproto/AuthData.h
+++ b/td/mtproto/AuthData.h
@@ -12,7 +12,7 @@
 #include "td/utils/Slice.h"
 #include "td/utils/Status.h"
 
-#include <set>
+#include <array>
 
 namespace td {
 namespace mtproto {
@@ -37,13 +37,18 @@ void parse(ServerSalt &salt, ParserT &parser) {
   salt.valid_until = parser.fetch_double();
 }
 
+Status check_message_id_duplicates(int64 *saved_message_ids, size_t max_size, size_t &end_pos, int64 message_id);
+
+template <size_t max_size>
 class MessageIdDuplicateChecker {
  public:
-  Status check(int64 message_id);
+  Status check(int64 message_id) {
+    return check_message_id_duplicates(&saved_message_ids_[0], max_size, end_pos_, message_id);
+  }
 
  private:
-  static constexpr size_t MAX_SAVED_MESSAGE_IDS = 1000;
-  std::set<int64> saved_message_ids_;
+  std::array<int64, 2 * max_size> saved_message_ids_;
+  size_t end_pos_ = 0;
 };
 
 class AuthData {
@@ -274,8 +279,8 @@ class AuthData {
 
   std::vector<ServerSalt> future_salts_;
 
-  MessageIdDuplicateChecker duplicate_checker_;
-  MessageIdDuplicateChecker updates_duplicate_checker_;
+  MessageIdDuplicateChecker<1000> duplicate_checker_;
+  MessageIdDuplicateChecker<1000> updates_duplicate_checker_;
 
   void update_salt(double now);
 };