diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 4475e880f..6211aff33 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -291,7 +291,7 @@ sub slice {
     while (@{$self->layers} && !@{$self->get_layer(0)->slices}) {
         shift @{$self->layers};
         for (my $i = 0; $i <= $#{$self->layers}; $i++) {
-            $self->get_layer($i)->id( $self->get_layer($i)->id-1 );
+            $self->get_layer($i)->set_id( $self->get_layer($i)->id-1 );
         }
     }
     
diff --git a/xs/src/libslic3r/Layer.cpp b/xs/src/libslic3r/Layer.cpp
index 38935fced..2e1a8c50e 100644
--- a/xs/src/libslic3r/Layer.cpp
+++ b/xs/src/libslic3r/Layer.cpp
@@ -6,7 +6,7 @@
 
 namespace Slic3r {
 
-Layer::Layer(int id, PrintObject *object, coordf_t height, coordf_t print_z,
+Layer::Layer(size_t id, PrintObject *object, coordf_t height, coordf_t print_z,
         coordf_t slice_z)
 :   _id(id),
     _object(object),
@@ -35,12 +35,18 @@ Layer::~Layer()
     this->clear_regions();
 }
 
-int
-Layer::id()
+size_t
+Layer::id() const
 {
     return this->_id;
 }
 
+void
+Layer::set_id(size_t id)
+{
+    this->_id = id;
+}
+
 PrintObject*
 Layer::object()
 {
@@ -147,7 +153,7 @@ REGISTER_CLASS(Layer, "Layer");
 #endif
 
 
-SupportLayer::SupportLayer(int id, PrintObject *object, coordf_t height,
+SupportLayer::SupportLayer(size_t id, PrintObject *object, coordf_t height,
         coordf_t print_z, coordf_t slice_z)
 :   Layer(id, object, height, print_z, slice_z)
 {
diff --git a/xs/src/libslic3r/Layer.hpp b/xs/src/libslic3r/Layer.hpp
index 5f6a6baa0..c21ffa1c8 100644
--- a/xs/src/libslic3r/Layer.hpp
+++ b/xs/src/libslic3r/Layer.hpp
@@ -72,7 +72,8 @@ class Layer {
     friend class PrintObject;
 
     public:
-    int id();
+    size_t id() const;
+    void set_id(size_t id);
     PrintObject* object();
 
     Layer *upper_layer;
@@ -97,11 +98,11 @@ class Layer {
     template <class T> bool any_bottom_region_slice_contains(const T &item) const;
     
     protected:
-    int _id;     // sequential number of layer, 0-based
+    size_t _id;     // sequential number of layer, 0-based
     PrintObject *_object;
 
 
-    Layer(int id, PrintObject *object, coordf_t height, coordf_t print_z,
+    Layer(size_t id, PrintObject *object, coordf_t height, coordf_t print_z,
         coordf_t slice_z);
     virtual ~Layer();
 
@@ -119,7 +120,7 @@ class SupportLayer : public Layer {
     ExtrusionEntityCollection support_interface_fills;
 
     protected:
-    SupportLayer(int id, PrintObject *object, coordf_t height, coordf_t print_z,
+    SupportLayer(size_t id, PrintObject *object, coordf_t height, coordf_t print_z,
         coordf_t slice_z);
     virtual ~SupportLayer();
 };
diff --git a/xs/xsp/Layer.xsp b/xs/xsp/Layer.xsp
index ffc9f9af8..02ac5fc2b 100644
--- a/xs/xsp/Layer.xsp
+++ b/xs/xsp/Layer.xsp
@@ -35,6 +35,7 @@
     // owned by PrintObject, no constructor/destructor
 
     int id();
+    void set_id(int id);
     Ref<PrintObject> object();
     Ref<Layer> upper_layer()
         %code%{ RETVAL = THIS->upper_layer; %};
@@ -89,6 +90,7 @@
     // copies of some Layer methods, because the parameter wrapper code
     // gets confused about getting a Layer::Support instead of a Layer
     int id();
+    void set_id(int id);
     Ref<PrintObject> object();
     Ref<SupportLayer> upper_layer()
         %code%{ RETVAL = (SupportLayer*)THIS->upper_layer; %};