diff --git a/src/render/software/CanvasPixelShader.cpp b/src/render/software/CanvasPixelShader.cpp
index 43f1940..318d071 100644
--- a/src/render/software/CanvasPixelShader.cpp
+++ b/src/render/software/CanvasPixelShader.cpp
@@ -16,8 +16,8 @@ int CanvasPixelShader::processParallelUnit(int unit)
 {
     // Locate the chunk we work on
     int prev_sub_chunk_size = chunk_size * 2;
-    int chunk_x = unit % chunks_x;
-    int chunk_y = unit / chunks_x;
+    int chunk_x = unit / chunks_y;
+    int chunk_y = unit % chunks_y;
     int base_x = chunk_x * chunk_size;
     int base_y = chunk_y * chunk_size;
     int limit_x = portion->getWidth() - base_x;
@@ -26,11 +26,12 @@ int CanvasPixelShader::processParallelUnit(int unit)
     limit_x = (limit_x > chunk_size) ? chunk_size : limit_x;
     limit_y = (limit_y > chunk_size) ? chunk_size : limit_y;
 
+    // Iterate on sub-chunks
     for (int x = 0; x < limit_x; x += sub_chunk_size)
     {
         for (int y = 0; y < limit_y; y += sub_chunk_size)
         {
-            if (x % prev_sub_chunk_size != 0 or y % prev_sub_chunk_size != 0)
+            if (sub_chunk_size == chunk_size or x % prev_sub_chunk_size != 0 or y % prev_sub_chunk_size != 0)
             {
                 // Resolve the pixel color
                 const CanvasPixel &pixel = portion->at(base_x + x, base_y + y);
@@ -42,7 +43,15 @@ int CanvasPixelShader::processParallelUnit(int unit)
                     const Rasterizer &rasterizer = renderer.getRasterizer(fragment.getClient());
                     composite.mask(rasterizer.shadeFragment(fragment));
                 }
-                portion->setColor(base_x + x, base_y + y, composite);
+
+                // Fill the square area
+                for (int fx = 0; fx + x < limit_x and fx < sub_chunk_size; fx++)
+                {
+                    for (int fy = 0; fy + y < limit_y and fy < sub_chunk_size; fy++)
+                    {
+                        portion->setColor(base_x + x + fx, base_y + y + fy, composite);
+                    }
+                }
             }
         }
     }
diff --git a/src/system/ParallelWork.cpp b/src/system/ParallelWork.cpp
index a80bb0a..c77aca3 100644
--- a/src/system/ParallelWork.cpp
+++ b/src/system/ParallelWork.cpp
@@ -66,8 +66,8 @@ protected:
             if (unit >= 0)
             {
                 work->worker->processParallelUnit(unit);
-                work->returnThread(this);
                 unit = -1;
+                work->returnThread(this);
             }
         }
     }