diff --git a/lib/Slic3r/ExPolygon.pm b/lib/Slic3r/ExPolygon.pm
index fd1af58b..c58af979 100644
--- a/lib/Slic3r/ExPolygon.pm
+++ b/lib/Slic3r/ExPolygon.pm
@@ -32,6 +32,11 @@ sub clone {
     Storable::dclone($_[0])
 }
 
+sub threadsafe_clone {
+    my $self = shift;
+    return (ref $self)->new(map $_->threadsafe_clone, @$self);
+}
+
 sub contour {
     my $self = shift;
     return $self->[0];
@@ -303,7 +308,7 @@ has 'expolygons' => (is => 'ro', default => sub { [] });
 sub clone {
     my $self = shift;
     return (ref $self)->new(
-        expolygons => [ map $_->clone, @{$self->expolygons} ],
+        expolygons => [ map $_->threadsafe_clone, @{$self->expolygons} ],
     );
 }
 
diff --git a/lib/Slic3r/Point.pm b/lib/Slic3r/Point.pm
index 233f60f3..4e86995e 100644
--- a/lib/Slic3r/Point.pm
+++ b/lib/Slic3r/Point.pm
@@ -24,6 +24,11 @@ sub clone {
     Storable::dclone($_[0])
 }
 
+sub threadsafe_clone {
+    my $self = shift;
+    return (ref $self)->new(@$self);
+}
+
 sub coincides_with {
     my $self = shift;
     my ($point) = @_;
diff --git a/lib/Slic3r/Polyline.pm b/lib/Slic3r/Polyline.pm
index f2a9cbd7..fd4bd571 100644
--- a/lib/Slic3r/Polyline.pm
+++ b/lib/Slic3r/Polyline.pm
@@ -22,6 +22,11 @@ sub clone {
     Storable::dclone($_[0])
 }
 
+sub threadsafe_clone {
+    my $self = shift;
+    return (ref $self)->new(map $_->threadsafe_clone, @$self);
+}
+
 sub serialize {
     my $self = shift;
     return pack 'l*', map @$_, @$self;
diff --git a/lib/Slic3r/TriangleMesh.pm b/lib/Slic3r/TriangleMesh.pm
index b4624250..e0698b4a 100644
--- a/lib/Slic3r/TriangleMesh.pm
+++ b/lib/Slic3r/TriangleMesh.pm
@@ -607,7 +607,7 @@ sub horizontal_projection {
     
     my @f = ();
     foreach my $facet (@{$self->facets}) {
-        push @f, Slic3r::Polygon->new([ map [ @{$self->vertices->[$_]}[X,Y] ], @$facet ]);
+        push @f, Slic3r::Polygon->new(map [ @{$self->vertices->[$_]}[X,Y] ], @$facet);
     }
     
     my $scale_vector = Math::Clipper::integerize_coordinate_sets({ bits => 32 }, @f);