diff --git a/tdutils/td/utils/FlatHashMapLinear.h b/tdutils/td/utils/FlatHashMapLinear.h
index 79f08d7d9..4d07751c6 100644
--- a/tdutils/td/utils/FlatHashMapLinear.h
+++ b/tdutils/td/utils/FlatHashMapLinear.h
@@ -163,10 +163,13 @@ class FlatHashTable {
   struct FlatHashTableInner {
     uint32 used_node_count_;
     uint32 bucket_count_mask_;
+    uint32 begin_bucket_;
+    uint32 padding_;
     NodeT nodes_[1];
   };
 
-  static constexpr size_t OFFSET = 2 * sizeof(uint32);
+  static constexpr size_t OFFSET = 4 * sizeof(uint32);
+  static constexpr uint32 INVALID_BUCKET = 0xFFFFFFFF;
 
   static NodeT *allocate_nodes(uint32 size) {
     DCHECK(size >= 8);
@@ -179,6 +182,7 @@ class FlatHashTable {
     }
     // inner->used_node_count_ = 0;
     inner->bucket_count_mask_ = size - 1;
+    inner->begin_bucket_ = INVALID_BUCKET;
     return nodes;
   }
 
@@ -387,11 +391,14 @@ class FlatHashTable {
     if (empty()) {
       return end();
     }
-    auto bucket = Random::fast_uint32() & get_bucket_count_mask();
-    while (nodes_[bucket].empty()) {
-      next_bucket(bucket);
+    auto &begin_bucket = get_inner()->begin_bucket_;
+    if (begin_bucket == INVALID_BUCKET) {
+      begin_bucket = Random::fast_uint32() & get_bucket_count_mask();
+      while (nodes_[begin_bucket].empty()) {
+        next_bucket(begin_bucket);
+      }
     }
-    return Iterator(nodes_ + bucket, this);
+    return Iterator(nodes_ + begin_bucket, this);
   }
   Iterator end() {
     return Iterator(nullptr, this);
@@ -539,6 +546,7 @@ class FlatHashTable {
     } else if (unlikely(get_used_node_count() * 5 > get_bucket_count_mask() * 3)) {
       resize(2 * get_bucket_count_mask() + 2);
     }
+    invalidate_iterators();
   }
 
   void try_shrink() {
@@ -546,6 +554,7 @@ class FlatHashTable {
     if (unlikely(get_used_node_count() * 10 < get_bucket_count_mask() && get_bucket_count_mask() > 7)) {
       resize(normalize((get_used_node_count() + 1) * 5 / 3 + 1));
     }
+    invalidate_iterators();
   }
 
   static uint32 normalize(uint32 size) {
@@ -615,6 +624,10 @@ class FlatHashTable {
       }
     }
   }
+
+  inline void invalidate_iterators() {
+    get_inner()->begin_bucket_ = INVALID_BUCKET;
+  }
 };
 
 template <class KeyT, class ValueT, class HashT = std::hash<KeyT>, class EqT = std::equal_to<KeyT>>