diff --git a/src/db/db/dbPolygonGenerators.cc b/src/db/db/dbPolygonGenerators.cc
index ddaf33268c..f339611ed1 100644
--- a/src/db/db/dbPolygonGenerators.cc
+++ b/src/db/db/dbPolygonGenerators.cc
@@ -410,6 +410,8 @@ PolygonGenerator::begin_scanline (db::Coord y)
   m_open_pos = m_open.begin ();
   m_y = y;
 
+  m_prev_stitch_index = std::numeric_limits<size_t>::max ();
+
 #ifdef DEBUG_POLYGON_GENERATOR
   printf ("m_open=");
   for (open_map_type::const_iterator o = m_open.begin (); o != m_open.end (); ++o) {
@@ -820,27 +822,68 @@ PolygonGenerator::join_contours (db::Coord x)
         tl_assert (c1.size () >= 2);
 
         PGPolyContour::iterator ins = cprev.end ();
-        db::Coord xprev = 0;
-        db::Edge eprev;
 
-#if 1
+        PGPolyContour::iterator ii = ins;
+        --ii;
+        PGPolyContour::iterator iii = ii;
+        --iii;
+
         //  shallow analysis: insert the cutline at the end of the sequence - this may
         //  cut lines collinear with contour edges
 
-        eprev = db::Edge (*(ins - 2), *(ins - 1));
-        xprev = db::coord_traits<db::Coord>::rounded (edge_xaty (db::Edge (*(ins - 2), *(ins - 1)), m_y));
-#else
-        //  deep analysis: determine insertion point: pick the one where the cutline is shortest
+        db::Edge eprev = db::Edge (*iii, *ii);
+        db::Coord xprev = db::coord_traits<db::Coord>::rounded (edge_xaty (eprev, m_y));
+
+#if 1  //  experimental
+        if (m_prev_stitch_index == iprev) {
+
+          auto i = m_prev_stitch_ins;
+          ii = i;
+          iii = --ii;
+          --iii;
+
+          if (ii->y () >= m_y) {
+
+            db::Edge ecut (*iii, *ii);
+            db::Coord xcut = db::coord_traits<db::Coord>::rounded (edge_xaty (ecut, m_y));
+
+            if (iii->y () < m_y && xcut < c1.back ().x () && xcut > xprev) {
+              xprev = xcut;
+              eprev = ecut;
+              ins = i;
+            }
+
+          }
+
+        } else {
+
+          //  deep analysis: determine insertion point: pick the one where the cutline is shortest
+          //  CAUTION: this may introduce a O(2) complexity in the number of holes along the x axis
+
+          while (true) {
+
+            auto i = ii;
+
+            ii = iii;
+            if (ii == cprev.begin ()) {
+              break;
+            }
 
-        for (PGPolyContour::iterator i = ins; i > cprev.begin () + 1; --i) {
+            --iii;
 
-          db::Edge ecut (i[-2], i[-1]);
-          db::Coord xcut = db::coord_traits<db::Coord>::rounded (edge_xaty (db::Edge (i[-2], i[-1]), m_y));
+            if (ii->y () >= m_y) {
+
+              db::Edge ecut (*iii, *ii);
+              db::Coord xcut = db::coord_traits<db::Coord>::rounded (edge_xaty (ecut, m_y));
+
+              if (iii->y () < m_y && xcut < c1.back ().x () && xcut > xprev) {
+                xprev = xcut;
+                eprev = ecut;
+                ins = i;
+              }
+
+            }
 
-          if (ins == i || (i[-1].y () >= m_y && i[-2].y () < m_y && xcut < c1.back ().x () && xcut > xprev)) {
-            xprev = xcut;
-            eprev = ecut;
-            ins = i;
           }
 
         }
@@ -864,6 +907,11 @@ PolygonGenerator::join_contours (db::Coord x)
         }
 
         ins = cprev.insert (ins, pprev);
+
+        //  remember the insertion point - it may be a candidate to attach the next hole
+        m_prev_stitch_ins = ins;
+        m_prev_stitch_index = iprev;
+
         ++ins;
         if (eprev.p2 () != pprev) {
           cprev.insert (ins, eprev.p2 ());
diff --git a/src/db/db/dbPolygonGenerators.h b/src/db/db/dbPolygonGenerators.h
index cc34c8fce6..b576812f54 100644
--- a/src/db/db/dbPolygonGenerators.h
+++ b/src/db/db/dbPolygonGenerators.h
@@ -183,6 +183,8 @@ class DB_PUBLIC PolygonGenerator
   db::SimplePolygon m_spoly;
   static bool ms_compress;
   bool m_compress;
+  size_t m_prev_stitch_index;
+  std::list<db::Point>::iterator m_prev_stitch_ins;
 
   void join_contours (db::Coord x);
   void produce_poly (const PGPolyContour &c);
diff --git a/src/plugins/streamers/gds2/unit_tests/dbGDS2WriterTests.cc b/src/plugins/streamers/gds2/unit_tests/dbGDS2WriterTests.cc
index 4e62f3aa03..091a134728 100644
--- a/src/plugins/streamers/gds2/unit_tests/dbGDS2WriterTests.cc
+++ b/src/plugins/streamers/gds2/unit_tests/dbGDS2WriterTests.cc
@@ -1192,7 +1192,7 @@ TEST(121)
 {
   db::GDS2WriterOptions opt;
   opt.max_vertex_count = 4;
-  run_test (_this, "t121.oas.gz", "t121_au.gds.gz", true, opt);
+  run_test (_this, "t121.oas.gz", "t121_au_2.gds.gz", true, opt);
 }
 
 //  Meta info
diff --git a/src/plugins/streamers/pcb/unit_tests/dbGerberImport.cc b/src/plugins/streamers/pcb/unit_tests/dbGerberImport.cc
index ea4bb68ac0..3fb4c1ddbf 100644
--- a/src/plugins/streamers/pcb/unit_tests/dbGerberImport.cc
+++ b/src/plugins/streamers/pcb/unit_tests/dbGerberImport.cc
@@ -33,7 +33,7 @@
 
 #include <stdlib.h>
 
-static void run_test (tl::TestBase *_this, const char *dir)
+static void run_test (tl::TestBase *_this, const char *dir, const char *au_file = "au.oas.gz")
 {
   if (! tl::XMLParser::is_available ()) {
     throw tl::CancelException ();
@@ -53,7 +53,7 @@ static void run_test (tl::TestBase *_this, const char *dir)
     reader.read (layout, options);
   }
 
-  db::compare_layouts (_this, layout, tl::testdata_private () + "/pcb/" + dir + "/au.oas.gz", db::WriteOAS, 1);
+  db::compare_layouts (_this, layout, tl::testdata_private () + "/pcb/" + dir + "/" + au_file, db::WriteOAS, 1);
 }
 
 TEST(0_Metadata)
@@ -167,7 +167,7 @@ TEST(1)
 
 TEST(2)
 {
-  run_test (_this, "allegro");
+  run_test (_this, "allegro", "au_2.oas.gz");
 }
 
 TEST(3)
@@ -199,13 +199,13 @@ TEST(7)
 TEST(8)
 {
   test_is_long_runner ();
-  run_test (_this, "microchip-2");
+  run_test (_this, "microchip-2", "au_2.oas.gz");
 }
 
 TEST(9)
 {
   test_is_long_runner ();
-  run_test (_this, "microchip-3");
+  run_test (_this, "microchip-3", "au_2.oas.gz");
 }
 
 TEST(10)
@@ -236,7 +236,7 @@ TEST(14)
 
 TEST(15)
 {
-  run_test (_this, "gerbv_examples/polarity");
+  run_test (_this, "gerbv_examples/polarity", "au_2.oas.gz");
 }
 
 TEST(16)
@@ -294,7 +294,7 @@ TEST(25)
 TEST(26)
 {
   test_is_long_runner ();
-  run_test (_this, "pos-neg");
+  run_test (_this, "pos-neg", "au_2.oas.gz");
 }
 
 TEST(27)
@@ -334,12 +334,12 @@ TEST(X2_2e)
 
 TEST(X2_2f)
 {
-  run_test (_this, "x2-2f");
+  run_test (_this, "x2-2f", "au_2.oas.gz");
 }
 
 TEST(X2_2g)
 {
-  run_test (_this, "x2-2g");
+  run_test (_this, "x2-2g", "au_2.oas.gz");
 }
 
 TEST(X2_2h)
@@ -364,7 +364,7 @@ TEST(X2_2k)
 
 TEST(X2_3)
 {
-  run_test (_this, "x2-3");
+  run_test (_this, "x2-3", "au_2.oas.gz");
 }
 
 TEST(X2_4)
diff --git a/testdata/algo/deep_region_au3.gds b/testdata/algo/deep_region_au3.gds
index e2e935ba88..406c175bce 100644
Binary files a/testdata/algo/deep_region_au3.gds and b/testdata/algo/deep_region_au3.gds differ
diff --git a/testdata/algo/deep_region_au3b.gds b/testdata/algo/deep_region_au3b.gds
index e741130cf5..e3f7a4493b 100644
Binary files a/testdata/algo/deep_region_au3b.gds and b/testdata/algo/deep_region_au3b.gds differ
diff --git a/testdata/algo/flat_region_au3.gds b/testdata/algo/flat_region_au3.gds
index 74fba6e4fa..77e4e30a11 100644
Binary files a/testdata/algo/flat_region_au3.gds and b/testdata/algo/flat_region_au3.gds differ
diff --git a/testdata/algo/flat_region_au3b.gds b/testdata/algo/flat_region_au3b.gds
index b6040526f4..28e9a43621 100644
Binary files a/testdata/algo/flat_region_au3b.gds and b/testdata/algo/flat_region_au3b.gds differ
diff --git a/testdata/bool/special2_au1.oas b/testdata/bool/special2_au1.oas
index a5f502f42c..0e47dce3a1 100644
Binary files a/testdata/bool/special2_au1.oas and b/testdata/bool/special2_au1.oas differ
diff --git a/testdata/bool/special2_au1_tz.oas b/testdata/bool/special2_au1_tz.oas
index 3290873a0a..cebd60d150 100644
Binary files a/testdata/bool/special2_au1_tz.oas and b/testdata/bool/special2_au1_tz.oas differ
diff --git a/testdata/bool/special2_au4.oas b/testdata/bool/special2_au4.oas
index e8580a4f14..13771eeeac 100644
Binary files a/testdata/bool/special2_au4.oas and b/testdata/bool/special2_au4.oas differ
diff --git a/testdata/bool/special2_au5.oas b/testdata/bool/special2_au5.oas
index 50fa6a864e..ea1f9fd1d8 100644
Binary files a/testdata/bool/special2_au5.oas and b/testdata/bool/special2_au5.oas differ
diff --git a/testdata/bool/special2_au5_tz.oas b/testdata/bool/special2_au5_tz.oas
index a374b17aa3..90ca8dc3c1 100644
Binary files a/testdata/bool/special2_au5_tz.oas and b/testdata/bool/special2_au5_tz.oas differ
diff --git a/testdata/bool/special3_au1.oas b/testdata/bool/special3_au1.oas
index 3f666f44ac..580886862a 100644
Binary files a/testdata/bool/special3_au1.oas and b/testdata/bool/special3_au1.oas differ
diff --git a/testdata/bool/special3_au2.oas b/testdata/bool/special3_au2.oas
index b0bcee8d71..9bdc9f3db0 100644
Binary files a/testdata/bool/special3_au2.oas and b/testdata/bool/special3_au2.oas differ
diff --git a/testdata/bool/special3_au5.oas b/testdata/bool/special3_au5.oas
index e4f0f1e8fd..f3b5a9976e 100644
Binary files a/testdata/bool/special3_au5.oas and b/testdata/bool/special3_au5.oas differ
diff --git a/testdata/bool/twobool9_au1.oas b/testdata/bool/twobool9_au1.oas
index 8b2353b7c0..e3f139eea3 100644
Binary files a/testdata/bool/twobool9_au1.oas and b/testdata/bool/twobool9_au1.oas differ
diff --git a/testdata/bool/xor7_max_au1.oas b/testdata/bool/xor7_max_au1.oas
index fce7269528..73aa257f66 100644
Binary files a/testdata/bool/xor7_max_au1.oas and b/testdata/bool/xor7_max_au1.oas differ
diff --git a/testdata/bool/xor7_max_au2.oas b/testdata/bool/xor7_max_au2.oas
index fce7269528..73aa257f66 100644
Binary files a/testdata/bool/xor7_max_au2.oas and b/testdata/bool/xor7_max_au2.oas differ