diff --git a/lib/Slic3r/Model.pm b/lib/Slic3r/Model.pm
index 162c3a3d1..789fbc373 100644
--- a/lib/Slic3r/Model.pm
+++ b/lib/Slic3r/Model.pm
@@ -104,32 +104,13 @@ sub duplicate_objects {
     $self->arrange_objects($distance, $bb);
 }
 
-# arrange objects preserving their instance count
-# but altering their instance positions
-sub arrange_objects {
-    my ($self, $distance, $bb) = @_;
-    
-    # get the (transformed) size of each instance so that we take
-    # into account their different transformations when packing
-    my @instance_sizes = ();
-    foreach my $object (@{$self->objects}) {
-        push @instance_sizes, map $object->instance_bounding_box($_)->size, 0..$#{$object->instances};
-    }
-    
-    my @positions = $self->_arrange(\@instance_sizes, $distance, $bb);
-    
-    foreach my $object (@{$self->objects}) {
-        $_->set_offset(Slic3r::Pointf->new(@{shift @positions})) for @{$object->instances};
-        $object->update_bounding_box;
-    }
-}
-
 # duplicate the entire model preserving instance relative positions
 sub duplicate {
     my ($self, $copies_num, $distance, $bb) = @_;
     
-    my $model_size = $self->bounding_box->size;
-    my @positions = $self->_arrange([ map $model_size, 2..$copies_num ], $distance, $bb);
+    my $model_size = Slic3r::Pointf->new(@{$self->bounding_box->size}[X,Y]);
+    $bb //= Slic3r::Geometry::BoundingBoxf->new;
+    my @positions = @{$self->_arrange([ map $model_size, 2..$copies_num ], $distance, $bb)};
     
     # note that this will leave the object count unaltered
     
@@ -148,23 +129,6 @@ sub duplicate {
     }
 }
 
-sub _arrange {
-    my ($self, $sizes, $distance, $bb) = @_;
-
-    $bb //= Slic3r::Geometry::BoundingBoxf->new;
-    
-    # we supply unscaled data to arrange()
-    return @{Slic3r::Geometry::arrange(
-        scalar(@$sizes),                # number of parts
-        Slic3r::Pointf->new(
-            max(map $_->x, @$sizes),        # cell width
-            max(map $_->y, @$sizes),        # cell height  ,
-        ),
-        $distance,                      # distance between cells
-        $bb,                            # bounding box of the area to fill (can be undef)
-    )};
-}
-
 sub print_info {
     my $self = shift;
     $_->print_info for @{$self->objects};
diff --git a/xs/src/libslic3r/Geometry.cpp b/xs/src/libslic3r/Geometry.cpp
index 827029aa0..62a6d8f7c 100644
--- a/xs/src/libslic3r/Geometry.cpp
+++ b/xs/src/libslic3r/Geometry.cpp
@@ -186,7 +186,6 @@ arrange(size_t total_parts, Pointf part, coordf_t dist, const BoundingBoxf &bb)
     // this is how many cells we have available into which to put parts
     size_t cellw = floor((area.x + dist) / part.x);
     size_t cellh = floor((area.x + dist) / part.x);
-    
     if (total_parts > (cellw * cellh))
         CONFESS("%zu parts won't fit in your print area!\n", total_parts);
     
diff --git a/xs/src/libslic3r/Model.cpp b/xs/src/libslic3r/Model.cpp
index 01c907fad..851a3b08b 100644
--- a/xs/src/libslic3r/Model.cpp
+++ b/xs/src/libslic3r/Model.cpp
@@ -239,6 +239,42 @@ Model::raw_mesh() const
     return mesh;
 }
 
+Pointfs
+Model::_arrange(const Pointfs &sizes, coordf_t dist, const BoundingBoxf &bb) const
+{
+    // we supply unscaled data to arrange()
+    return Slic3r::Geometry::arrange(
+        sizes.size(),               // number of parts
+        BoundingBoxf(sizes).max,    // width and height of a single cell
+        dist,                       // distance between cells
+        bb                          // bounding box of the area to fill
+    );
+}
+
+/*  arrange objects preserving their instance count
+    but altering their instance positions */
+void
+Model::arrange_objects(coordf_t dist, BoundingBoxf bb)
+{
+    // get the (transformed) size of each instance so that we take
+    // into account their different transformations when packing
+    Pointfs instance_sizes;
+    for (ModelObjectPtrs::const_iterator o = this->objects.begin(); o != this->objects.end(); ++o) {
+        for (size_t i = 0; i < (*o)->instances.size(); ++i) {
+            instance_sizes.push_back((*o)->instance_bounding_box(i).size());
+        }
+    }
+    
+    Pointfs positions = this->_arrange(instance_sizes, dist, bb);
+    
+    for (ModelObjectPtrs::const_iterator o = this->objects.begin(); o != this->objects.end(); ++o) {
+        for (ModelInstancePtrs::const_iterator i = (*o)->instances.begin(); i != (*o)->instances.end(); ++i) {
+            (*i)->offset = positions.back();
+            positions.pop_back();
+        }
+    }
+}
+
 #ifdef SLIC3RXS
 REGISTER_CLASS(Model, "Model");
 #endif
diff --git a/xs/src/libslic3r/Model.hpp b/xs/src/libslic3r/Model.hpp
index d802ae8e7..64b22d837 100644
--- a/xs/src/libslic3r/Model.hpp
+++ b/xs/src/libslic3r/Model.hpp
@@ -61,10 +61,8 @@ class Model
     TriangleMesh mesh() const;
     TriangleMesh raw_mesh() const;
     // std::string get_material_name(t_model_material_id material_id);
-
-    
-    private:
-    void _arrange(const std::vector<Size> &sizes, coordf_t distance, const BoundingBox &bb) const;
+    Pointfs _arrange(const Pointfs &sizes, coordf_t dist, const BoundingBoxf &bb) const;
+    void arrange_objects(coordf_t dist, BoundingBoxf bb = BoundingBoxf());
 };
 
 class ModelMaterial
diff --git a/xs/xsp/Model.xsp b/xs/xsp/Model.xsp
index 183890967..ee54dbcb6 100644
--- a/xs/xsp/Model.xsp
+++ b/xs/xsp/Model.xsp
@@ -55,7 +55,6 @@
 
     // void duplicate_objects_grid(coordf_t x, coordf_t y, coordf_t distance);
     // void duplicate_objects(size_t copies_num, coordf_t distance, const BoundingBox &bb);
-    // void arrange_objects(coordf_t distance, const BoundingBox &bb);
     // void duplicate(size_t copies_num, coordf_t distance, const BoundingBox &bb);
     bool has_objects_with_no_instances();
     bool add_default_instances();
@@ -71,6 +70,12 @@
 
     ModelObjectPtrs* objects()
         %code%{ RETVAL = &THIS->objects; %};
+    
+    Pointfs _arrange(Pointfs sizes, double dist, BoundingBoxf* bb)
+        %code%{ RETVAL = THIS->_arrange(sizes, dist, *bb); %};
+    
+    void arrange_objects(double dist, BoundingBoxf* bb)
+        %code%{ THIS->arrange_objects(dist, *bb); %};
 };