diff --git a/lib/Slic3r/Geometry/Clipper.pm b/lib/Slic3r/Geometry/Clipper.pm
index bef2713da5..0c2cbfe35a 100644
--- a/lib/Slic3r/Geometry/Clipper.pm
+++ b/lib/Slic3r/Geometry/Clipper.pm
@@ -113,8 +113,8 @@ sub ex_int_offset2 {
 }
 
 sub collapse_ex {
-    my ($polygons, $width) = @_;
-    return ex_int_offset2($polygons, -$width/2, +$width/2);
+    my ($polygons, $width) = @_;use XXX; YYY 
+    return [ ex_int_offset2($polygons, -$width/2, +$width/2) ];
 }
 
 sub simplify_polygon {