diff --git a/drape_frontend/frontend_renderer.cpp b/drape_frontend/frontend_renderer.cpp
index 340be008e2..26114579aa 100755
--- a/drape_frontend/frontend_renderer.cpp
+++ b/drape_frontend/frontend_renderer.cpp
@@ -1005,7 +1005,7 @@ void FrontendRenderer::MergeBuckets()
     dp::GLState state = group->GetState();
     if (state.GetDepthLayer() == dp::GLState::GeometryLayer && !group->IsPendingOnDelete())
     {
-      MergedGroupKey const key = MergedGroupKey(state, group->GetTileKey());
+      MergedGroupKey const key(state, group->GetTileKey());
       forMerge[key].push_back(move(m_renderGroups[i]));
     }
     else
diff --git a/drape_frontend/tile_key.hpp b/drape_frontend/tile_key.hpp
index 57d1ad0e7c..6738f3f40d 100755
--- a/drape_frontend/tile_key.hpp
+++ b/drape_frontend/tile_key.hpp
@@ -23,9 +23,17 @@ struct TileKey
   TileKey(int x, int y, int zoomLevel);
   TileKey(TileKey const & key, uint64_t generation);
 
+  // Operators < and == do not consider parameters m_styleZoomLevel and m_generation.
+  // m_styleZoomLevel is used to work around FeaturesFetcher::ForEachFeatureID which is
+  // not able to return correct rects on 18,19 zoom levels. So m_zoomLevel can not be
+  // more than 17 for all subsystems except of styling.
+  // m_generation is used to determine a generation of geometry for this tile key.
+  // Geometry with different generations must be able to group by (x, y, zoomlevel).
   bool operator < (TileKey const & other) const;
   bool operator == (TileKey const & other) const;
 
+  // This method implements strict comparison of tile keys. It's necessary to merger of
+  // batches which must not merge batches with different m_styleZoomLevel and m_generation.
   bool LessStrict(TileKey const & other) const;
 
   m2::RectD GetGlobalRect(bool considerStyleZoom = false) const;
@@ -33,6 +41,7 @@ struct TileKey
   int m_x;
   int m_y;
   int m_zoomLevel;
+
   int m_styleZoomLevel;
   uint64_t m_generation;
 };