diff --git a/src/db/db/dbPolygonTools.cc b/src/db/db/dbPolygonTools.cc
index 0202ee908..db18b69d3 100644
--- a/src/db/db/dbPolygonTools.cc
+++ b/src/db/db/dbPolygonTools.cc
@@ -1685,6 +1685,20 @@ AreaMap::bbox () const
 // -------------------------------------------------------------------------
 //  Implementation of rasterize
 
+static bool edge_is_partially_left_of (const db::Edge &e, const db::Edge &e_original, db::Coord x)
+{
+  Coord xmin = db::edge_xmin (e);
+  if (xmin < x) {
+    return true;
+  } else if (xmin == x && e_original.dx () != 0) {
+    //  the skew edge is cut partially rendering a straight vertical line (due to rounding)
+    //  which we will count as "left of"
+    return true;
+  } else {
+    return false;
+  }
+}
+
 bool
 rasterize (const db::Polygon &polygon, db::AreaMap &am)
 {
@@ -1801,7 +1815,7 @@ rasterize (const db::Polygon &polygon, db::AreaMap &am)
         for (std::vector <db::Edge>::iterator e = cc; e != ff; ++e) {
 
           std::pair<bool, db::Edge> ec = e->clipped (left);
-          if (ec.first && db::edge_xmin (ec.second) < x) {
+          if (ec.first && edge_is_partially_left_of (ec.second, *e, x)) {
             a += area_type (ec.second.dy ()) * area_type (px);
           }
 
@@ -1818,7 +1832,7 @@ rasterize (const db::Polygon &polygon, db::AreaMap &am)
         for (std::vector <db::Edge>::iterator e = cc; e != ff; ++e) {
 
           std::pair<bool, db::Edge> ec = e->clipped (cell);
-          if (ec.first && db::edge_xmin (ec.second) < xx) {
+          if (ec.first && edge_is_partially_left_of (ec.second, *e, xx)) {
             aa += (area_type (ec.second.dy ()) * area_type (2 * xx - (ec.second.p2 ().x () + ec.second.p1 ().x ()))) / 2;
             a += area_type (ec.second.dy ()) * area_type (px);
           }
@@ -1832,7 +1846,7 @@ rasterize (const db::Polygon &polygon, db::AreaMap &am)
         for (std::vector <db::Edge>::iterator e = cc; e != ff; ++e) {
 
           std::pair<bool, db::Edge> ec = e->clipped (cell);
-          if (ec.first && db::edge_xmin (ec.second) < xx) {
+          if (ec.first && edge_is_partially_left_of (ec.second, *e, xx)) {
             aa += (area_type (ec.second.dy ()) * area_type (2 * xx - (ec.second.p2 ().x () + ec.second.p1 ().x ()))) / 2;
           }
 
@@ -1843,7 +1857,7 @@ rasterize (const db::Polygon &polygon, db::AreaMap &am)
         for (std::vector <db::Edge>::iterator e = cc; e != fff; ++e) {
 
           std::pair<bool, db::Edge> wide_ec = e->clipped (wide_cell);
-          if (wide_ec.first && db::edge_xmin (wide_ec.second) < x + dx) {
+          if (wide_ec.first && edge_is_partially_left_of (wide_ec.second, *e, x + dx)) {
             a += area_type (wide_ec.second.dy ()) * area_type (px);
           }
 
diff --git a/src/db/unit_tests/dbFillToolTests.cc b/src/db/unit_tests/dbFillToolTests.cc
index ded8efe5b..3447929ad 100644
--- a/src/db/unit_tests/dbFillToolTests.cc
+++ b/src/db/unit_tests/dbFillToolTests.cc
@@ -313,3 +313,35 @@ TEST(4c)
   CHECKPOINT();
   db::compare_layouts (_this, ly, tl::testdata () + "/algo/fill_tool_au4c.gds");
 }
+
+//  issue #1309
+TEST(5)
+{
+  db::Layout ly;
+  {
+    std::string fn (tl::testdata ());
+    fn += "/algo/fill_tool5.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (ly);
+  }
+
+  db::cell_index_type fill_cell = ly.cell_by_name ("FILL_CELL").second;
+  db::cell_index_type top_cell = ly.cell_by_name ("TOP").second;
+  unsigned int fill_layer = ly.get_layer (db::LayerProperties (1, 0));
+
+  db::Region fill_region (db::RecursiveShapeIterator (ly, ly.cell (top_cell), fill_layer));
+
+  db::Region remaining_polygons;
+
+  db::Vector rs (50, 0);
+  db::Vector cs (0, 50);
+  db::Box fc_box (db::Point (), db::Point (rs.x (), cs.y ()));
+  db::fill_region (&ly.cell (top_cell), fill_region, fill_cell, fc_box, rs, cs, db::Point (), false, &remaining_polygons);
+
+  unsigned int l100 = ly.insert_layer (db::LayerProperties (100, 0));
+  remaining_polygons.insert_into (&ly, top_cell, l100);
+
+  CHECKPOINT();
+  db::compare_layouts (_this, ly, tl::testdata () + "/algo/fill_tool_au5.oas", db::WriteOAS);
+}
diff --git a/testdata/algo/fill_tool5.gds b/testdata/algo/fill_tool5.gds
new file mode 100644
index 000000000..ca90c13e1
Binary files /dev/null and b/testdata/algo/fill_tool5.gds differ
diff --git a/testdata/algo/fill_tool_au5.oas b/testdata/algo/fill_tool_au5.oas
new file mode 100644
index 000000000..f4040eedc
Binary files /dev/null and b/testdata/algo/fill_tool_au5.oas differ