diff --git a/topography_generator/generator.cpp b/topography_generator/generator.cpp
index 87733f0af7..b82be52c18 100644
--- a/topography_generator/generator.cpp
+++ b/topography_generator/generator.cpp
@@ -67,6 +67,9 @@ private:
 
   Altitude GetMedianValue(ms::LatLon const & pos)
   {
+    if (!m_srtmManager.GetTile(pos).IsValid())
+      return kInvalidAltitude;
+
     // Look around the position with invalid altitude
     // and return median of surrounding valid altitudes.
     double const step = kTileSizeInDegree / kArcSecondsInDegree;
@@ -151,7 +154,12 @@ public:
   {
     auto movedPos = pos;
     if (m_moveFromBorderFn(movedPos))
-      return m_originalProvider.GetValue(movedPos);
+    {
+      // Check that we have original neighboring tile, use filtered if haven't.
+      auto const alt = m_originalProvider.GetValue(movedPos);
+      if (alt != kInvalidAltitude)
+        return alt;
+    }
     return m_filteredProvider.GetValue(pos);
   }
 
diff --git a/topography_generator/marching_squares/marching_squares.hpp b/topography_generator/marching_squares/marching_squares.hpp
index 2be6114bf4..dfe9d582f2 100644
--- a/topography_generator/marching_squares/marching_squares.hpp
+++ b/topography_generator/marching_squares/marching_squares.hpp
@@ -50,8 +50,13 @@ public:
       contoursBuilder.BeginLine();
       for (size_t j = 0; j < m_stepsCountLon; ++j)
       {
-        auto const pos = ms::LatLon(m_leftBottom.m_lat + m_step * i, m_leftBottom.m_lon + m_step * j);
-        Square<ValueType> square(pos, m_step, result.m_minValue, m_valueStep, m_valuesProvider);
+        auto const leftBottom = ms::LatLon(m_leftBottom.m_lat + m_step * i,
+                                           m_leftBottom.m_lon + m_step * j);
+        // Use std::min to prevent floating-point number precision error.
+        auto const rightTop = ms::LatLon(std::min(leftBottom.m_lat + m_step, m_rightTop.m_lat),
+                                         std::min(leftBottom.m_lon + m_step, m_rightTop.m_lon));
+
+        Square<ValueType> square(leftBottom, rightTop, result.m_minValue, m_valueStep, m_valuesProvider);
         square.SetDebugId(m_debugId);
         square.GenerateSegments(contoursBuilder);
       }
diff --git a/topography_generator/marching_squares/square.hpp b/topography_generator/marching_squares/square.hpp
index 27ee94bd9b..e3d344f526 100644
--- a/topography_generator/marching_squares/square.hpp
+++ b/topography_generator/marching_squares/square.hpp
@@ -9,15 +9,16 @@ template <typename ValueType>
 class Square
 {
 public:
-  Square(ms::LatLon const & leftBottom, double size,
+  Square(ms::LatLon const & leftBottom,
+         ms::LatLon const & rightTop,
          ValueType minValue, ValueType valueStep,
          ValuesProvider<ValueType> & valuesProvider)
     : m_minValue(minValue)
     , m_valueStep(valueStep)
     , m_left(leftBottom.m_lon)
-    , m_right(leftBottom.m_lon + size)
+    , m_right(rightTop.m_lon)
     , m_bottom(leftBottom.m_lat)
-    , m_top(leftBottom.m_lat + size)
+    , m_top(rightTop.m_lat)
   {
     static_assert(std::is_integral<ValueType>::value, "Only integral types are supported.");