diff --git a/xs/src/ClipperUtils.cpp b/xs/src/ClipperUtils.cpp
index 57216f0b2..c26370fe7 100644
--- a/xs/src/ClipperUtils.cpp
+++ b/xs/src/ClipperUtils.cpp
@@ -442,14 +442,24 @@ static void traverse_pt(ClipperLib::PolyNodes &nodes, Slic3r::Polygons &retval)
     }
 }
 
-void simplify_polygons(const Slic3r::Polygons &subject, Slic3r::Polygons &retval)
+void simplify_polygons(const Slic3r::Polygons &subject, Slic3r::Polygons &retval, bool preserve_collinear)
 {
     // convert into Clipper polygons
     ClipperLib::Paths* input_subject = new ClipperLib::Paths();
     Slic3rMultiPoints_to_ClipperPaths(subject, *input_subject);
     
     ClipperLib::Paths* output = new ClipperLib::Paths();
-    ClipperLib::SimplifyPolygons(*input_subject, *output, ClipperLib::pftNonZero);
+    
+    if (preserve_collinear) {
+        ClipperLib::Clipper c;
+        c.PreserveCollinear(true);
+        c.StrictlySimple(true);
+        c.AddPaths(*input_subject, ClipperLib::ptSubject, true);
+        c.Execute(ClipperLib::ctUnion, *output, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
+    } else {
+        ClipperLib::SimplifyPolygons(*input_subject, *output, ClipperLib::pftNonZero);
+    }
+    
     delete input_subject;
     
     // convert into Slic3r polygons
diff --git a/xs/src/ClipperUtils.hpp b/xs/src/ClipperUtils.hpp
index 4bd62c6c7..3f3e01bbe 100644
--- a/xs/src/ClipperUtils.hpp
+++ b/xs/src/ClipperUtils.hpp
@@ -98,7 +98,7 @@ void union_pt(const Slic3r::Polygons &subject, ClipperLib::PolyTree &retval, boo
 void union_pt_chained(const Slic3r::Polygons &subject, Slic3r::Polygons &retval, bool safety_offset_ = false);
 static void traverse_pt(ClipperLib::PolyNodes &nodes, Slic3r::Polygons &retval);
 
-void simplify_polygons(const Slic3r::Polygons &subject, Slic3r::Polygons &retval);
+void simplify_polygons(const Slic3r::Polygons &subject, Slic3r::Polygons &retval, bool preserve_collinear = false);
 
 void safety_offset(ClipperLib::Paths* &subject);
 
diff --git a/xs/src/ExPolygon.cpp b/xs/src/ExPolygon.cpp
index 095d3e73d..85af87525 100644
--- a/xs/src/ExPolygon.cpp
+++ b/xs/src/ExPolygon.cpp
@@ -239,6 +239,8 @@ ExPolygon::get_trapezoids2(Polygons* polygons, double angle) const
         polygon->rotate(-(PI/2 - angle), Point(0,0));
 }
 
+// While this triangulates successfully, it's NOT a constrained triangulation
+// as it will create more vertices on the boundaries than the ones supplied.
 void
 ExPolygon::triangulate(Polygons* polygons) const
 {
@@ -252,33 +254,44 @@ ExPolygon::triangulate(Polygons* polygons) const
 }
 
 void
-ExPolygon::triangulate2(Polygons* polygons) const
+ExPolygon::triangulate_pp(Polygons* polygons) const
 {
     // convert polygons
     std::list<TPPLPoly> input;
     
-    // contour
-    {
-        TPPLPoly p;
-        p.Init(this->contour.points.size());
-        for (Points::const_iterator point = this->contour.points.begin(); point != this->contour.points.end(); ++point) {
-            p[ point-this->contour.points.begin() ].x = point->x;
-            p[ point-this->contour.points.begin() ].y = point->y;
-        }
-        p.SetHole(false);
-        input.push_back(p);
-    }
+    Polygons pp = *this;
+    simplify_polygons(pp, pp, true);
+    ExPolygons expp;
+    union_(pp, expp);
     
-    // holes
-    for (Polygons::const_iterator hole = this->holes.begin(); hole != this->holes.end(); ++hole) {
-        TPPLPoly p;
-        p.Init(hole->points.size());
-        for (Points::const_iterator point = hole->points.begin(); point != hole->points.end(); ++point) {
-            p[ point-hole->points.begin() ].x = point->x;
-            p[ point-hole->points.begin() ].y = point->y;
+    for (ExPolygons::const_iterator ex = expp.begin(); ex != expp.end(); ++ex) {
+        // contour
+        {
+            TPPLPoly p;
+            p.Init(ex->contour.points.size());
+            //printf("%zu\n0\n", ex->contour.points.size());
+            for (Points::const_iterator point = ex->contour.points.begin(); point != ex->contour.points.end(); ++point) {
+                p[ point-ex->contour.points.begin() ].x = point->x;
+                p[ point-ex->contour.points.begin() ].y = point->y;
+                //printf("%ld %ld\n", point->x, point->y);
+            }
+            p.SetHole(false);
+            input.push_back(p);
+        }
+    
+        // holes
+        for (Polygons::const_iterator hole = ex->holes.begin(); hole != ex->holes.end(); ++hole) {
+            TPPLPoly p;
+            p.Init(hole->points.size());
+            //printf("%zu\n1\n", hole->points.size());
+            for (Points::const_iterator point = hole->points.begin(); point != hole->points.end(); ++point) {
+                p[ point-hole->points.begin() ].x = point->x;
+                p[ point-hole->points.begin() ].y = point->y;
+                //printf("%ld %ld\n", point->x, point->y);
+            }
+            p.SetHole(true);
+            input.push_back(p);
         }
-        p.SetHole(true);
-        input.push_back(p);
     }
     
     // perform triangulation
diff --git a/xs/src/ExPolygon.hpp b/xs/src/ExPolygon.hpp
index 07ab7c9b8..b9857b8c2 100644
--- a/xs/src/ExPolygon.hpp
+++ b/xs/src/ExPolygon.hpp
@@ -32,7 +32,7 @@ class ExPolygon
     void get_trapezoids2(Polygons* polygons) const;
     void get_trapezoids2(Polygons* polygons, double angle) const;
     void triangulate(Polygons* polygons) const;
-    void triangulate2(Polygons* polygons) const;
+    void triangulate_pp(Polygons* polygons) const;
     
     #ifdef SLIC3RXS
     void from_SV(SV* poly_sv);
diff --git a/xs/src/TriangleMesh.cpp b/xs/src/TriangleMesh.cpp
index 79e97b3ef..a80f14921 100644
--- a/xs/src/TriangleMesh.cpp
+++ b/xs/src/TriangleMesh.cpp
@@ -923,7 +923,7 @@ TriangleMeshSlicer::cut(float z, TriangleMesh* upper, TriangleMesh* lower)
         // triangulate section
         Polygons triangles;
         for (ExPolygons::const_iterator expolygon = section.begin(); expolygon != section.end(); ++expolygon)
-            expolygon->triangulate2(&triangles);
+            expolygon->triangulate_pp(&triangles);
         
         // convert triangles to facets and append them to mesh
         for (Polygons::const_iterator polygon = triangles.begin(); polygon != triangles.end(); ++polygon) {
@@ -951,7 +951,7 @@ TriangleMeshSlicer::cut(float z, TriangleMesh* upper, TriangleMesh* lower)
         // triangulate section
         Polygons triangles;
         for (ExPolygons::const_iterator expolygon = section.begin(); expolygon != section.end(); ++expolygon)
-            expolygon->triangulate2(&triangles);
+            expolygon->triangulate_pp(&triangles);
         
         // convert triangles to facets and append them to mesh
         for (Polygons::const_iterator polygon = triangles.begin(); polygon != triangles.end(); ++polygon) {
diff --git a/xs/t/04_expolygon.t b/xs/t/04_expolygon.t
index 18ea03d1d..5c10651f8 100644
--- a/xs/t/04_expolygon.t
+++ b/xs/t/04_expolygon.t
@@ -134,7 +134,7 @@ is $expolygon->area, 100*100-20*20, 'area';
 }
 
 {
-    my $triangles = $expolygon->triangulate2;
+    my $triangles = $expolygon->triangulate_pp;
     is scalar(@$triangles), 8, 'expected number of triangles';
     is sum(map $_->area, @$triangles), $expolygon->area, 'sum of triangles area equals original expolygon area';
 }
diff --git a/xs/xsp/ExPolygon.xsp b/xs/xsp/ExPolygon.xsp
index 9d6eff536..aada66185 100644
--- a/xs/xsp/ExPolygon.xsp
+++ b/xs/xsp/ExPolygon.xsp
@@ -36,8 +36,8 @@
         %code{% THIS->get_trapezoids2(&RETVAL, angle); %};
     Polygons triangulate()
         %code{% THIS->triangulate(&RETVAL); %};
-    Polygons triangulate2()
-        %code{% THIS->triangulate2(&RETVAL); %};
+    Polygons triangulate_pp()
+        %code{% THIS->triangulate_pp(&RETVAL); %};
 %{
 
 ExPolygon*