diff --git a/lib/Slic3r/Geometry/Clipper.pm b/lib/Slic3r/Geometry/Clipper.pm
index 142acbd0e..e8af9e4d1 100644
--- a/lib/Slic3r/Geometry/Clipper.pm
+++ b/lib/Slic3r/Geometry/Clipper.pm
@@ -94,6 +94,7 @@ sub union_ex {
     my ($polygons, $jointype, $safety_offset) = @_;
     $jointype = PFT_NONZERO unless defined $jointype;
     $clipper->clear;
+    $polygons = $polygons->arrayref if ref $polygons eq 'Slic3r::ExPolygon::XS';
     $clipper->add_subject_polygons($safety_offset ? safety_offset($polygons) : $polygons);
     return [
         map Slic3r::ExPolygon::XS->new($_->{outer}, @{$_->{holes}}),
diff --git a/lib/Slic3r/TriangleMesh.pm b/lib/Slic3r/TriangleMesh.pm
index 5f58d0e20..8a0ef5706 100644
--- a/lib/Slic3r/TriangleMesh.pm
+++ b/lib/Slic3r/TriangleMesh.pm
@@ -533,6 +533,7 @@ sub horizontal_projection {
     my $scale_vector = Math::Clipper::integerize_coordinate_sets({ bits => 32 }, @f);
     $_->make_counter_clockwise for @f;  # do this after scaling, as winding order might change while doing that
     my $union = union_ex([ Slic3r::Geometry::Clipper::offset(\@f, 10000) ]);
+    $union = [ map $_->arrayref, @$union ];
     Math::Clipper::unscale_coordinate_sets($scale_vector, $_) for @$union;
     return $union;
 }
diff --git a/xs/src/Point.hpp b/xs/src/Point.hpp
index 4b14b9115..6b5ea3b06 100644
--- a/xs/src/Point.hpp
+++ b/xs/src/Point.hpp
@@ -13,9 +13,9 @@ extern "C" {
 class Point
 {
     public:
-    unsigned long x;
-    unsigned long y;
-    Point(unsigned long _x = 0, unsigned long _y = 0): x(_x), y(_y) {};
+    long x;
+    long y;
+    Point(long _x = 0, long _y = 0): x(_x), y(_y) {};
     void rotate(double angle, Point* center);
 };
 
@@ -24,8 +24,8 @@ Point::rotate(double angle, Point* center)
 {
     double cur_x = (double)x;
     double cur_y = (double)y;
-    x = (unsigned long)( (double)center->x + cos(angle) * (cur_x - (double)center->x) - sin(angle) * (cur_y - (double)center->y) );
-    y = (unsigned long)( (double)center->y + cos(angle) * (cur_y - (double)center->y) + sin(angle) * (cur_x - (double)center->x) );
+    x = (long)( (double)center->x + cos(angle) * (cur_x - (double)center->x) - sin(angle) * (cur_y - (double)center->y) );
+    y = (long)( (double)center->y + cos(angle) * (cur_y - (double)center->y) + sin(angle) * (cur_x - (double)center->x) );
 }
 
 SV*