diff --git a/pcbnew/plot_board_layers.cpp b/pcbnew/plot_board_layers.cpp
index a979b97308..bb5df56afe 100644
--- a/pcbnew/plot_board_layers.cpp
+++ b/pcbnew/plot_board_layers.cpp
@@ -8,7 +8,7 @@
 /*
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
- * Copyright (C) 1992-2017 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 1992-2019 KiCad Developers, see AUTHORS.txt for contributors.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -582,6 +582,19 @@ void PlotStandardLayer( BOARD *aBoard, PLOTTER* aPlotter,
             if( candidate->GetNetCode() != zone->GetNetCode() )
                 continue;
 
+            // Merging zones of the same net can be done only for areas
+            // having compatible settings for drawings:
+            // use or not outline thickness, and if using outline thickness,
+            // having the same thickness
+            // becuase after merging only one outline thickness is used
+            if( candidate->GetFilledPolysUseThickness() != zone->GetFilledPolysUseThickness() )
+                // Should not happens, because usually the same option is used for filling
+                continue;
+
+            if( zone->GetFilledPolysUseThickness() &&
+                ( candidate->GetMinThickness() != zone->GetMinThickness() ) )
+                continue;
+
             plotted.insert( candidate );
             aggregateArea.BooleanAdd( candidate->GetFilledPolysList(), SHAPE_POLY_SET::PM_FAST );
         }
diff --git a/pcbnew/plot_brditems_plotter.cpp b/pcbnew/plot_brditems_plotter.cpp
index f6afcd6c83..cf7718ba17 100644
--- a/pcbnew/plot_brditems_plotter.cpp
+++ b/pcbnew/plot_brditems_plotter.cpp
@@ -659,12 +659,13 @@ void BRDITEMS_PLOTTER::PlotFilledAreas( ZONE_CONTAINER* aZone, SHAPE_POLY_SET& p
     m_plotter->SetColor( getColor( aZone->GetLayer() ) );
 
     /* Plot all filled areas: filled areas have a filled area and a thick
-     * outline we must plot the filled area itself ( as a filled polygon
-     * OR a set of segments ) and plot the thick outline itself,
-     * if the thickness has meaning (at least is > 1)
+     * outline (depending on the fill area option we must plot the filled area itself
+     * and plot the thick outline itself, if the thickness has meaning (at least is > 1)
      *
      * in non filled mode the outline is plotted, but not the filling items
      */
+    int outline_thickness = aZone->GetFilledPolysUseThickness() ? aZone->GetMinThickness() : 0;
+
     for( auto ic = polysList.CIterate(); ic; ++ic )
     {
         wxPoint pos( ic->x, ic->y );
@@ -677,8 +678,6 @@ void BRDITEMS_PLOTTER::PlotFilledAreas( ZONE_CONTAINER* aZone, SHAPE_POLY_SET& p
                 cornerList.push_back( cornerList[0] );
 
             // Plot the current filled area and its outline
-            int outline_thickness = aZone->GetFilledPolysUseThickness() ? aZone->GetMinThickness() : 0;
-
             if( GetPlotMode() == FILLED )
             {
                 m_plotter->PlotPoly( cornerList, FILLED_SHAPE, outline_thickness, &gbr_metadata );