diff --git a/td/telegram/OptionManager.cpp b/td/telegram/OptionManager.cpp
index 27ccde50c..6ff9a0fc3 100644
--- a/td/telegram/OptionManager.cpp
+++ b/td/telegram/OptionManager.cpp
@@ -60,6 +60,7 @@ OptionManager::OptionManager(Td *td)
   all_options["utc_time_offset"] = PSTRING() << 'I' << Clocks::tz_offset();
   for (const auto &name_value : all_options) {
     const string &name = name_value.first;
+    CHECK(!name.empty());
     options_->set(name, name_value.second);
     if (!is_internal_option(name)) {
       send_closure(G()->td(), &Td::send_update,
diff --git a/tddb/td/db/SeqKeyValue.h b/tddb/td/db/SeqKeyValue.h
index 9870ac939..b12975cfb 100644
--- a/tddb/td/db/SeqKeyValue.h
+++ b/tddb/td/db/SeqKeyValue.h
@@ -6,11 +6,9 @@
 //
 #pragma once
 
-#include "td/utils/HashTableUtils.h"
+#include "td/utils/FlatHashMap.h"
 #include "td/utils/Slice.h"
 
-#include <unordered_map>
-
 namespace td {
 
 class SeqKeyValue {
@@ -24,6 +22,7 @@ class SeqKeyValue {
   ~SeqKeyValue() = default;
 
   SeqNo set(Slice key, Slice value) {
+    CHECK(!key.empty());
     auto it_ok = map_.emplace(key.str(), value.str());
     if (!it_ok.second) {
       if (it_ok.first->second == value) {
@@ -84,13 +83,19 @@ class SeqKeyValue {
     return map_.size();
   }
 
-  std::unordered_map<string, string, Hash<string>> get_all() const {
-    return map_;
+  FlatHashMap<string, string> get_all() const {
+    FlatHashMap<string, string> result;
+    result.reserve(map_.size());
+    for (auto &it : map_) {
+      result.emplace(it.first, it.second);
+    }
+    return result;
   }
 
  private:
-  std::unordered_map<string, string, Hash<string>> map_;
+  FlatHashMap<string, string> map_;
   SeqNo current_id_ = 0;
+
   SeqNo next_seq_no() {
     return ++current_id_;
   }
diff --git a/tddb/td/db/TsSeqKeyValue.h b/tddb/td/db/TsSeqKeyValue.h
index ebb413289..ec56b9738 100644
--- a/tddb/td/db/TsSeqKeyValue.h
+++ b/tddb/td/db/TsSeqKeyValue.h
@@ -8,11 +8,10 @@
 
 #include "td/db/SeqKeyValue.h"
 
-#include "td/utils/HashTableUtils.h"
+#include "td/utils/FlatHashMap.h"
 #include "td/utils/port/RwMutex.h"
 #include "td/utils/Slice.h"
 
-#include <unordered_map>
 #include <utility>
 
 namespace td {
@@ -69,7 +68,7 @@ class TsSeqKeyValue {
     return kv_.size();
   }
 
-  std::unordered_map<string, string, Hash<string>> get_all() const {
+  FlatHashMap<string, string> get_all() const {
     auto lock = rw_mutex_.lock_write().move_as_ok();
     return kv_.get_all();
   }