diff --git a/lib/Slic3r/Geometry/Clipper.pm b/lib/Slic3r/Geometry/Clipper.pm
index 2b090a8bb..164d5fc3e 100644
--- a/lib/Slic3r/Geometry/Clipper.pm
+++ b/lib/Slic3r/Geometry/Clipper.pm
@@ -45,18 +45,6 @@ sub offset2 {
     return @$offsets;
 }
 
-sub diff_ex {
-    my ($subject, $clip, $safety_offset) = @_;
-    
-    $clipper->clear;
-    $clipper->add_subject_polygons(_convert($subject));
-    $clipper->add_clip_polygons($safety_offset ? _convert(safety_offset($clip)) : _convert($clip));
-    return [
-        map Slic3r::ExPolygon->new($_->{outer}, @{$_->{holes}}),
-            @{ $clipper->ex_execute(CT_DIFFERENCE, PFT_NONZERO, PFT_NONZERO) },
-    ];
-}
-
 sub diff {
     my ($subject, $clip, $safety_offset) = @_;
     
diff --git a/xs/t/11_clipper.t b/xs/t/11_clipper.t
index 1da3de557..3bff3b804 100644
--- a/xs/t/11_clipper.t
+++ b/xs/t/11_clipper.t
@@ -4,24 +4,24 @@ use strict;
 use warnings;
 
 use Slic3r::XS;
-use Test::More tests => 2;
+use Test::More tests => 3;
 
 my $square = [  # ccw
-    [100, 100],
     [200, 100],
     [200, 200],
     [100, 200],
+    [100, 100],
 ];
 my $hole_in_square = [  # cw
+    [160, 140],
     [140, 140],
     [140, 160],
     [160, 160],
-    [160, 140],
 ];
 my $expolygon = Slic3r::ExPolygon->new($square, $hole_in_square);
 
 {
-    my $result = @{Slic3r::Geometry::Clipper::offset_ex([ @$expolygon ], 5)};
+    my $result = Slic3r::Geometry::Clipper::offset_ex([ @$expolygon ], 5);
     is_deeply $result->[0]->pp, [ [
         [205, 95],
         [205, 205],
@@ -36,7 +36,7 @@ my $expolygon = Slic3r::ExPolygon->new($square, $hole_in_square);
 }
 
 {
-    my $result = @{Slic3r::Geometry::Clipper::offset2_ex([ @$expolygon ], 5, -2)};
+    my $result = Slic3r::Geometry::Clipper::offset2_ex([ @$expolygon ], 5, -2);
     is_deeply $result->[0]->pp, [ [
         [203, 97],
         [203, 203],
@@ -50,4 +50,11 @@ my $expolygon = Slic3r::ExPolygon->new($square, $hole_in_square);
     ] ], 'offset_ex';
 }
 
+{
+    my $polygon1 = Slic3r::Polygon->new(@$square);
+    my $polygon2 = Slic3r::Polygon->new(reverse @$hole_in_square);
+    my $result = Slic3r::Geometry::Clipper::diff_ex([$polygon1], [$polygon2]);
+    is_deeply $result->[0]->pp, $expolygon->pp, 'diff_ex';
+}
+
 __END__
diff --git a/xs/xsp/Clipper.xsp b/xs/xsp/Clipper.xsp
index 324da1b53..019639925 100644
--- a/xs/xsp/Clipper.xsp
+++ b/xs/xsp/Clipper.xsp
@@ -74,4 +74,41 @@ offset2_ex(polygons, delta1, delta2, scale = 100000, joinType = ClipperLib::jtMi
     OUTPUT:
         RETVAL
 
+ExPolygons
+diff_ex(subject, clip, safety_offset = false)
+    Polygons    subject
+    Polygons    clip
+    bool        safety_offset
+    CODE:
+        // read input
+        ClipperLib::Polygons* input_subject = new ClipperLib::Polygons();
+        ClipperLib::Polygons* input_clip    = new ClipperLib::Polygons();
+        Slic3rPolygons_to_ClipperPolygons(subject, *input_subject);
+        Slic3rPolygons_to_ClipperPolygons(clip,    *input_clip);
+        
+        // perform safety offset
+        if (safety_offset) {
+            // SafetyOffset(*input_clip);
+        }
+        
+        // init Clipper
+        ClipperLib::Clipper clipper;
+        clipper.Clear();
+        
+        // add polygons
+        clipper.AddPolygons(*input_subject, ClipperLib::ptSubject);
+        delete input_subject;
+        clipper.AddPolygons(*input_clip, ClipperLib::ptClip);
+        delete input_clip;
+        
+        // perform operation
+        ClipperLib::PolyTree* polytree = new ClipperLib::PolyTree();
+        clipper.Execute(ClipperLib::ctDifference, *polytree, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
+        
+        // convert into ExPolygons
+        PolyTreeToExPolygons(*polytree, RETVAL);
+        delete polytree;
+    OUTPUT:
+        RETVAL
+
 %}