diff --git a/src/GUI/Plater.hpp b/src/GUI/Plater.hpp
index 2d42295a5..c74f9d87f 100644
--- a/src/GUI/Plater.hpp
+++ b/src/GUI/Plater.hpp
@@ -21,6 +21,7 @@
 namespace Slic3r { namespace GUI {
 
 using UndoOperation = int;
+using obj_index = unsigned int;
 
 class Plater2DObject;
 class Plate2D;
diff --git a/src/GUI/Plater/Plater2DObject.hpp b/src/GUI/Plater/Plater2DObject.hpp
index 3a1772cfb..1bd5b97ba 100644
--- a/src/GUI/Plater/Plater2DObject.hpp
+++ b/src/GUI/Plater/Plater2DObject.hpp
@@ -8,6 +8,7 @@ public:
     std::string name {""};
     std::string identifier {""};
     bool selected {false};
+    int selected_instance {-1};
 };
 } } // Namespace Slic3r::GUI
 #endif