diff --git a/indexer/index.hpp b/indexer/index.hpp
index 2c390db385..d7c21ba0d5 100644
--- a/indexer/index.hpp
+++ b/indexer/index.hpp
@@ -120,7 +120,7 @@ private:
                                          pValue->m_factory);
 
         // iterate through intervals
-        CheckUniqueIndexes checkUnique;
+        CheckUniqueIndexes checkUnique(header.GetFormat() >= version::v5);
         MwmId const mwmID = handle.GetId();
 
         for (auto const & i : interval)
@@ -167,7 +167,7 @@ private:
                                          pValue->m_factory);
 
         // iterate through intervals
-        CheckUniqueIndexes checkUnique;
+        CheckUniqueIndexes checkUnique(header.GetFormat() >= version::v5);
         MwmId const mwmID = handle.GetId();
 
         for (auto const & i : interval)
diff --git a/indexer/unique_index.hpp b/indexer/unique_index.hpp
index 9578045fe1..41865773d0 100644
--- a/indexer/unique_index.hpp
+++ b/indexer/unique_index.hpp
@@ -2,39 +2,54 @@
 
 #include "../base/base.hpp"
 
+#include "../std/unordered_set.hpp"
 #include "../std/vector.hpp"
 
 
 class CheckUniqueIndexes
 {
+  unordered_set<uint32_t> m_s;
   vector<bool> m_v;
+  bool m_useBits;
 
-public:
   /// Add index to the set.
   /// @return true If index was absent.
   bool Add(uint32_t ind)
   {
-    if (m_v.size() <= ind)
-      m_v.resize(ind + 1);
-    bool const ret = !m_v[ind];
-    m_v[ind] = true;
-    return ret;
+    if (m_useBits)
+    {
+      if (m_v.size() <= ind)
+        m_v.resize(ind + 1);
+      bool const ret = !m_v[ind];
+      m_v[ind] = true;
+      return ret;
+    }
+    else
+      return m_s.insert(ind).second;
   }
 
   /// Remove index from the set.
   /// @return true If index was present.
   bool Remove(uint32_t ind)
   {
-    if (m_v.size() > ind)
+    if (m_useBits)
     {
-      bool const ret = m_v[ind];
-      m_v[ind] = false;
-      return ret;
+      if (m_v.size() > ind)
+      {
+        bool const ret = m_v[ind];
+        m_v[ind] = false;
+        return ret;
+      }
+      else
+        return false;
     }
     else
-      return false;
+      return (m_s.erase(ind) > 0);
   }
 
+public:
+  explicit CheckUniqueIndexes(bool useBits) : m_useBits(useBits) {}
+
   bool operator()(uint32_t ind)
   {
     return Add(ind);