diff --git a/base/CMakeLists.txt b/base/CMakeLists.txt
index 78b4bc815d..d4e2ad4bd4 100644
--- a/base/CMakeLists.txt
+++ b/base/CMakeLists.txt
@@ -42,6 +42,7 @@ set(
   set_operations.hpp
   shared_buffer_manager.cpp
   shared_buffer_manager.hpp
+  small_set.hpp
   src_point.cpp
   src_point.hpp
   stats.hpp
diff --git a/base/base.pro b/base/base.pro
index d8f90faf79..7eda31055f 100644
--- a/base/base.pro
+++ b/base/base.pro
@@ -66,6 +66,7 @@ HEADERS += \
     scope_guard.hpp \
     set_operations.hpp \
     shared_buffer_manager.hpp \
+    small_set.hpp \
     src_point.hpp \
     stats.hpp \
     std_serialization.hpp \
diff --git a/base/base_tests/CMakeLists.txt b/base/base_tests/CMakeLists.txt
index 7d3106daaa..2a31f84d0c 100644
--- a/base/base_tests/CMakeLists.txt
+++ b/base/base_tests/CMakeLists.txt
@@ -23,6 +23,7 @@ set(
   regexp_test.cpp
   rolling_hash_test.cpp
   scope_guard_test.cpp
+  small_set_test.cpp
   stl_add_test.cpp
   stl_helpers_test.cpp
   string_format_test.cpp
diff --git a/base/base_tests/base_tests.pro b/base/base_tests/base_tests.pro
index 32049b5282..a057e05ed7 100644
--- a/base/base_tests/base_tests.pro
+++ b/base/base_tests/base_tests.pro
@@ -33,6 +33,7 @@ SOURCES += \
   regexp_test.cpp \
   rolling_hash_test.cpp \
   scope_guard_test.cpp \
+  small_set_test.cpp \
   stl_add_test.cpp \
   stl_helpers_test.cpp \
   string_format_test.cpp \
diff --git a/base/base_tests/small_set_test.cpp b/base/base_tests/small_set_test.cpp
new file mode 100644
index 0000000000..bb2ae235cf
--- /dev/null
+++ b/base/base_tests/small_set_test.cpp
@@ -0,0 +1,74 @@
+#include "testing/testing.hpp"
+
+#include "base/small_set.hpp"
+
+#include <algorithm>
+#include <iterator>
+#include <vector>
+
+using namespace base;
+
+namespace
+{
+UNIT_TEST(SmallSet_Empty)
+{
+  SmallSet<0> set;
+  TEST_EQUAL(set.Size(), 0, ());
+}
+
+UNIT_TEST(SmallSet_Smoke)
+{
+  SmallSet<300> set;
+  TEST_EQUAL(set.Size(), 0, ());
+
+  set.Insert(0);
+  TEST_EQUAL(set.Size(), 1, ());
+  TEST(set.Contains(0), ());
+
+  set.Insert(0);
+  TEST_EQUAL(set.Size(), 1, ());
+  TEST(set.Contains(0), ());
+
+  set.Insert(5);
+  TEST_EQUAL(set.Size(), 2, ());
+  TEST(set.Contains(0), ());
+  TEST(set.Contains(5), ());
+
+  set.Insert(64);
+  TEST_EQUAL(set.Size(), 3, ());
+  TEST(set.Contains(0), ());
+  TEST(set.Contains(5), ());
+  TEST(set.Contains(64), ());
+
+  {
+    auto cur = set.begin();
+    auto end = set.end();
+    for (uint64_t i : {0, 5, 64})
+    {
+      TEST(cur != end, ());
+      TEST_EQUAL(*cur, i, ());
+      ++cur;
+    }
+    TEST(cur == end, ());
+  }
+
+  set.Remove(5);
+  TEST_EQUAL(set.Size(), 2, ());
+  TEST(set.Contains(0), ());
+  TEST(!set.Contains(5), ());
+  TEST(set.Contains(64), ());
+
+  set.Insert(297);
+  set.Insert(298);
+  set.Insert(299);
+  TEST_EQUAL(set.Size(), 5, ());
+
+  {
+    std::vector<uint64_t> const actual(set.begin(), set.end());
+    std::vector<uint64_t> const expected = {0, 64, 297, 298, 299};
+    TEST_EQUAL(actual, expected, ());
+  }
+
+  TEST_EQUAL(set.Size(), std::distance(set.begin(), set.end()), ());
+}
+}  // namespace
diff --git a/base/small_set.hpp b/base/small_set.hpp
new file mode 100644
index 0000000000..de1dad1406
--- /dev/null
+++ b/base/small_set.hpp
@@ -0,0 +1,167 @@
+#pragma once
+
+#include "base/assert.hpp"
+#include "base/bits.hpp"
+#include "base/macros.hpp"
+
+#include <cstdint>
+#include <iterator>
+#include <sstream>
+#include <string>
+
+namespace base
+{
+// A set of values less than |UpperBound|.
+//
+// Requires UpperBound + O(1) bits of memory.  All operations except
+// Clear() and iteration are O(1).  Clear() and iteration require
+// O(UpperBound) steps.
+//
+// *NOTE* This class *IS NOT* thread safe.
+template <uint64_t UpperBound>
+class SmallSet
+{
+public:
+  static uint64_t constexpr kNumBlocks = (UpperBound + 63) / 64;
+
+  class Iterator
+  {
+  public:
+    using difference_type = uint64_t;
+    using value_type = uint64_t;
+    using pointer = void;
+    using reference = void;
+    using iterator_category = std::forward_iterator_tag;
+
+    Iterator(uint64_t const * blocks, uint64_t current_block_index)
+      : m_blocks(blocks), m_current_block_index(current_block_index), m_current_block(0)
+    {
+      ASSERT_LESS_OR_EQUAL(current_block_index, kNumBlocks, ());
+      if (current_block_index < kNumBlocks)
+        m_current_block = m_blocks[current_block_index];
+      SkipZeroes();
+    }
+
+    bool operator==(Iterator const & rhs) const
+    {
+      return m_blocks == rhs.m_blocks && m_current_block_index == rhs.m_current_block_index &&
+             m_current_block == rhs.m_current_block;
+    }
+
+    bool operator!=(Iterator const & rhs) const { return !(*this == rhs); }
+
+    uint64_t operator*() const
+    {
+      ASSERT_NOT_EQUAL(m_current_block, 0, ());
+      auto const bit = m_current_block & -m_current_block;
+      return bits::PopCount(bit - 1) + m_current_block_index * 64;
+    }
+
+    Iterator const & operator++()
+    {
+      ASSERT(m_current_block_index < kNumBlocks, ());
+      ASSERT_NOT_EQUAL(m_current_block, 0, ());
+      m_current_block = m_current_block & (m_current_block - 1);
+      SkipZeroes();
+      return *this;
+    }
+
+  private:
+    void SkipZeroes()
+    {
+      ASSERT_LESS_OR_EQUAL(m_current_block_index, kNumBlocks, ());
+
+      if (m_current_block != 0 || m_current_block_index == kNumBlocks)
+        return;
+
+      do
+        ++m_current_block_index;
+      while (m_current_block_index < kNumBlocks && m_blocks[m_current_block_index] == 0);
+      if (m_current_block_index < kNumBlocks)
+        m_current_block = m_blocks[m_current_block_index];
+      else
+        m_current_block = 0;
+    }
+
+    uint64_t const * m_blocks;
+    uint64_t m_current_block_index;
+    uint64_t m_current_block;
+  };
+
+#define DEFINE_BLOCK_OFFSET(value)   \
+  uint64_t const block = value / 64; \
+  uint64_t const offset = value % 64
+
+  // This invalidates all iterators except end().
+  void Insert(uint64_t value)
+  {
+    ASSERT_LESS(value, UpperBound, ());
+
+    DEFINE_BLOCK_OFFSET(value);
+    auto const bit = kOne << offset;
+    m_size += (m_blocks[block] & bit) == 0;
+    m_blocks[block] |= bit;
+  }
+
+  // This invalidates all iterators except end().
+  void Remove(uint64_t value)
+  {
+    ASSERT_LESS(value, UpperBound, ());
+
+    DEFINE_BLOCK_OFFSET(value);
+    auto const bit = kOne << offset;
+    m_size -= (m_blocks[block] & bit) != 0;
+    m_blocks[block] &= ~bit;
+  }
+
+  bool Contains(uint64_t value) const
+  {
+    ASSERT_LESS(value, UpperBound, ());
+
+    DEFINE_BLOCK_OFFSET(value);
+    return m_blocks[block] & (kOne << offset);
+  }
+
+#undef DEFINE_BLOCK_OFFSET
+
+  uint64_t Size() const { return m_size; }
+
+  // This invalidates all iterators except end().
+  void Clear()
+  {
+    std::fill(std::begin(m_blocks), std::end(m_blocks), static_cast<uint64_t>(0));
+    m_size = 0;
+  }
+
+  Iterator begin() const { return Iterator(m_blocks, 0); }
+  Iterator cbegin() const { return Iterator(m_blocks, 0); }
+
+  Iterator end() const { return Iterator(m_blocks, kNumBlocks); }
+  Iterator cend() const { return Iterator(m_blocks, kNumBlocks); }
+
+private:
+  static uint64_t constexpr kOne = 1;
+
+  uint64_t m_blocks[kNumBlocks] = {};
+  uint64_t m_size = 0;
+};
+
+// static
+template <uint64_t UpperBound>
+uint64_t constexpr SmallSet<UpperBound>::kNumBlocks;
+
+// static
+template <uint64_t UpperBound>
+uint64_t constexpr SmallSet<UpperBound>::kOne;
+
+template<uint64_t UpperBound>
+std::string DebugPrint(SmallSet<UpperBound> const & set)
+{
+  std::ostringstream os;
+  os << "SmallSet<" << UpperBound << "> [" << set.Size() << ": ";
+  for (auto const & v : set)
+    os << v << " ";
+  os << "]";
+  return os.str();
+}
+}  // namespace base
diff --git a/search/feature_offset_match.hpp b/search/feature_offset_match.hpp
index cb88fbddf7..1c57683304 100644
--- a/search/feature_offset_match.hpp
+++ b/search/feature_offset_match.hpp
@@ -207,18 +207,18 @@ private:
 template <typename DFA>
 struct SearchTrieRequest
 {
-  inline bool IsLangExist(int8_t lang) const { return m_langs.count(lang) != 0; }
+  inline bool IsLangExist(int8_t lang) const { return m_langs.Contains(lang); }
 
   inline void Clear()
   {
     m_names.clear();
     m_categories.clear();
-    m_langs.clear();
+    m_langs.Clear();
   }
 
   vector<DFA> m_names;
   vector<strings::UniStringDFA> m_categories;
-  unordered_set<int8_t> m_langs;
+  QueryParams::Langs m_langs;
 };
 
 // Calls |toDo| for each feature accepted but at least one DFA.
diff --git a/search/processor.cpp b/search/processor.cpp
index ab6caeb387..9fab4d0e5c 100644
--- a/search/processor.cpp
+++ b/search/processor.cpp
@@ -677,7 +677,7 @@ void Processor::InitParams(QueryParams & params)
 
   auto & langs = params.GetLangs();
   for (int i = 0; i < LANG_COUNT; ++i)
-    langs.insert(GetLanguage(i));
+    langs.Insert(GetLanguage(i));
 
   RemoveStopWordsIfNeeded(params);
 
diff --git a/search/query_params.cpp b/search/query_params.cpp
index 573e4cffca..dec6d4ead4 100644
--- a/search/query_params.cpp
+++ b/search/query_params.cpp
@@ -54,7 +54,7 @@ void QueryParams::Clear()
   m_prefixToken.Clear();
   m_hasPrefix = false;
   m_typeIndices.clear();
-  m_langs.clear();
+  m_langs.Clear();
   m_scale = scales::GetUpperScale();
 }
 
@@ -135,7 +135,7 @@ string DebugPrint(QueryParams const & params)
   os << "QueryParams [ m_tokens=" << ::DebugPrint(params.m_tokens)
      << ", m_prefixToken=" << DebugPrint(params.m_prefixToken)
      << ", m_typeIndices=" << ::DebugPrint(params.m_typeIndices)
-     << ", m_langs=" << ::DebugPrint(params.m_langs) << " ]";
+     << ", m_langs=" << DebugPrint(params.m_langs) << " ]";
   return os.str();
 }
 
diff --git a/search/query_params.hpp b/search/query_params.hpp
index 42a890a288..480ebee23c 100644
--- a/search/query_params.hpp
+++ b/search/query_params.hpp
@@ -2,7 +2,10 @@
 
 #include "indexer/scales.hpp"
 
+#include "coding/multilang_utf8_string.hpp"
+
 #include "base/assert.hpp"
+#include "base/small_set.hpp"
 #include "base/string_utils.hpp"
 
 #include "std/cstdint.hpp"
@@ -20,7 +23,39 @@ class QueryParams
 public:
   using String = strings::UniString;
   using TypeIndices = vector<uint32_t>;
-  using Langs = unordered_set<int8_t>;
+
+  class Langs
+  {
+  public:
+    using Set = base::SmallSet<StringUtf8Multilang::kMaxSupportedLanguages>;
+    using Iterator = Set::Iterator;
+
+    void Insert(int8_t lang)
+    {
+      if (IsValid(lang))
+        m_set.Insert(lang);
+    }
+
+    bool Contains(int8_t lang) const { return IsValid(lang) ? m_set.Contains(lang) : false; }
+
+    void Clear() { m_set.Clear(); }
+
+    Iterator begin() const { return m_set.begin(); }
+    Iterator cbegin() const { return m_set.cbegin(); }
+
+    Iterator end() const { return m_set.end(); }
+    Iterator cend() const { return m_set.cend(); }
+
+  private:
+    friend string DebugPrint(Langs const & langs) { return DebugPrint(langs.m_set); }
+
+    bool IsValid(int8_t lang) const
+    {
+      return lang >= 0 && lang < StringUtf8Multilang::kMaxSupportedLanguages;
+    }
+
+    Set m_set;
+  };
 
   struct Token
   {
@@ -110,7 +145,7 @@ public:
 
   inline Langs & GetLangs() { return m_langs; }
   inline Langs const & GetLangs() const { return m_langs; }
-  inline bool LangExists(int8_t lang) const { return m_langs.count(lang) != 0; }
+  inline bool LangExists(int8_t lang) const { return m_langs.Contains(lang); }
 
   inline int GetScale() const { return m_scale; }