diff --git a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
index 398aebb52..98058ee17 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.cpp
@@ -60,11 +60,13 @@ void GLGizmoFlatten::data_changed(bool is_serializing)
 {
     const Selection &  selection    = m_parent.get_selection();
     const ModelObject *model_object = nullptr;
+    int                instance_id = -1;
     if (selection.is_single_full_instance() ||
         selection.is_from_single_object() ) {        
         model_object = selection.get_model()->objects[selection.get_object_idx()];
+        instance_id = selection.get_instance_idx();
     }    
-    set_flattening_data(model_object);
+    set_flattening_data(model_object, instance_id);
 }
 
 bool GLGizmoFlatten::on_init()
@@ -156,9 +158,9 @@ void GLGizmoFlatten::on_unregister_raycasters_for_picking()
     m_planes_casters.clear();
 }
 
-void GLGizmoFlatten::set_flattening_data(const ModelObject* model_object)
+void GLGizmoFlatten::set_flattening_data(const ModelObject* model_object, int instance_id)
 {
-    if (model_object != m_old_model_object) {
+    if (model_object != m_old_model_object || instance_id != m_old_instance_id) {
         m_planes.clear();
         on_unregister_raycasters_for_picking();
     }
@@ -363,6 +365,7 @@ void GLGizmoFlatten::update_planes()
     m_first_instance_scale = mo->instances.front()->get_scaling_factor();
     m_first_instance_mirror = mo->instances.front()->get_mirror();
     m_old_model_object = mo;
+    m_old_instance_id = m_c->selection_info()->get_active_instance();
 
     // And finally create respective VBOs. The polygon is convex with
     // the vertices in order, so triangulation is trivial.
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.hpp b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.hpp
index 1701b76a5..ff44fcd2d 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoFlatten.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoFlatten.hpp
@@ -39,6 +39,7 @@ private:
     std::vector<std::shared_ptr<SceneRaycasterItem>> m_planes_casters;
     bool m_mouse_left_down = false; // for detection left_up of this gizmo
     const ModelObject* m_old_model_object = nullptr;
+    int                m_old_instance_id{ -1 };
 
     void update_planes();
     bool is_plane_update_necessary() const;
@@ -46,7 +47,7 @@ private:
 public:
     GLGizmoFlatten(GLCanvas3D& parent, const std::string& icon_filename, unsigned int sprite_id);
 
-    void set_flattening_data(const ModelObject* model_object);
+    void set_flattening_data(const ModelObject* model_object, int instance_id);
         
     /// <summary>
     /// Apply rotation on select plane