diff --git a/src/slic3r/GUI/Gizmos/GLGizmoEmboss.cpp b/src/slic3r/GUI/Gizmos/GLGizmoEmboss.cpp
index 88f8ab6c81..64dc7cd1cb 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoEmboss.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoEmboss.cpp
@@ -397,12 +397,6 @@ ModelVolumePtrs prepare_volumes_to_slice(const ModelVolume &mv)
     }
     return result;
 }
-
-TransformationType get_transformation_type(const Selection &selection)
-{
-    assert(selection.is_single_full_object() || selection.is_single_volume());
-    return selection.is_single_volume() ? TransformationType::Local_Relative_Joint : TransformationType::Instance_Relative_Joint; // object
-}
 } // namespace
 
 bool GLGizmoEmboss::do_mirror(size_t axis)
@@ -429,7 +423,7 @@ bool GLGizmoEmboss::do_mirror(size_t axis)
         Selection &selection = m_parent.get_selection();
         selection.setup_cache();
 
-        auto selection_mirror_fnc = [&selection, &axis]() { selection.mirror((Axis) axis, get_transformation_type(selection)); };
+        auto selection_mirror_fnc = [&selection, &axis]() { selection.mirror((Axis) axis, get_drag_transformation_type(selection)); };
         selection_transform(selection, selection_mirror_fnc, m_volume);
 
         m_parent.do_mirror(L("Set Mirror"));
@@ -518,7 +512,7 @@ bool GLGizmoEmboss::on_mouse_for_rotation(const wxMouseEvent &mouse_event)
 
         // temporary rotation
         Selection& selection = m_parent.get_selection();
-        selection.rotate(Vec3d(0., 0., angle), get_transformation_type(selection));
+        selection.rotate(Vec3d(0., 0., angle), get_drag_transformation_type(selection));
 
         angle += *m_rotate_start_angle;
         // move to range <-M_PI, M_PI>
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSVG.cpp b/src/slic3r/GUI/Gizmos/GLGizmoSVG.cpp
index d85b0b909f..2064567ade 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSVG.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSVG.cpp
@@ -232,16 +232,6 @@ bool GLGizmoSVG::is_svg_object(const ModelVolume &volume) {
     return true;
 }
 
-namespace {
-TransformationType get_transformation_type(const Selection &selection)
-{
-    assert(selection.is_single_full_object() || selection.is_single_volume());
-    return selection.is_single_volume() ? 
-        TransformationType::Local_Relative_Independent :
-        TransformationType::Instance_Relative_Independent; // object
-}
-} // namespace
-
 bool GLGizmoSVG::on_mouse_for_rotation(const wxMouseEvent &mouse_event)
 {
     if (mouse_event.Moving()) return false;
@@ -265,7 +255,7 @@ bool GLGizmoSVG::on_mouse_for_rotation(const wxMouseEvent &mouse_event)
 
         Selection &selection = m_parent.get_selection();
         auto selection_rotate_fnc = [z_rotation, &selection]() { 
-            selection.rotate(Vec3d(0., 0., z_rotation), get_transformation_type(selection));
+            selection.rotate(Vec3d(0., 0., z_rotation), get_drag_transformation_type(selection));
         };
         selection_transform(selection, selection_rotate_fnc, m_volume);
         
@@ -1808,7 +1798,7 @@ void GLGizmoSVG::draw_size()
         selection.setup_cache();
 
         auto selection_scale_fnc = [&selection, rel_scale = *new_relative_scale]() {
-            selection.scale(rel_scale, get_transformation_type(selection));
+            selection.scale(rel_scale, get_drag_transformation_type(selection));
         };        
         selection_transform(selection, selection_scale_fnc, m_volume);
 
@@ -1969,7 +1959,7 @@ void GLGizmoSVG::draw_mirroring()
         selection.setup_cache();
 
         auto selection_mirror_fnc = [&selection, &axis](){
-            selection.mirror(axis, get_transformation_type(selection));
+            selection.mirror(axis, get_drag_transformation_type(selection));
         };
         selection_transform(selection, selection_mirror_fnc, m_volume);
 
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp b/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
index 428705ff88..a83a6456b6 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
@@ -175,7 +175,7 @@ void GLGizmoSimplify::on_render_input_window(float x, float y, float bottom_limi
     if (act_volume_ids.empty()) {
         stop_worker_thread_request();
         close();
-        if (! m_parent.get_selection().is_single_volume()) {
+        if (m_parent.get_selection().volumes_count() != 1) {
             MessageDialog msg((wxWindow*)wxGetApp().mainframe,
                 _L("Simplification is currently only allowed when a single part is selected"),
                 _L("Error"));
diff --git a/src/slic3r/GUI/SurfaceDrag.cpp b/src/slic3r/GUI/SurfaceDrag.cpp
index 251dee46cf..7f29414790 100644
--- a/src/slic3r/GUI/SurfaceDrag.cpp
+++ b/src/slic3r/GUI/SurfaceDrag.cpp
@@ -379,8 +379,9 @@ void do_local_z_rotate(GLCanvas3D &canvas, double relative_angle)
     assert(!selection.is_empty());
     if(selection.is_empty()) return;
 
-    assert(selection.is_single_full_object() || selection.is_single_volume());
-    if (!selection.is_single_full_object() && !selection.is_single_volume()) return;
+    bool is_single_volume = selection.volumes_count() == 1;
+    assert(is_single_volume);
+    if (!is_single_volume) return;
 
     // Fix angle for mirrored volume
     bool is_mirrored = false;
@@ -391,7 +392,6 @@ void do_local_z_rotate(GLCanvas3D &canvas, double relative_angle)
             if (instance != nullptr)
                 is_mirrored = has_reflection(instance->get_matrix());
         } else {
-            // selection.is_single_volume()
             const ModelVolume *volume = get_model_volume(*gl_volume, selection.get_model()->objects);
             if (volume != nullptr)
                 is_mirrored = has_reflection(volume->get_matrix());
@@ -404,9 +404,9 @@ void do_local_z_rotate(GLCanvas3D &canvas, double relative_angle)
     selection.setup_cache();
 
     auto selection_rotate_fnc = [&selection, &relative_angle](){
-        TransformationType transformation_type = selection.is_single_volume() ? 
-            TransformationType::Local_Relative_Independent : 
-            TransformationType::Instance_Relative_Independent;
+        TransformationType transformation_type = selection.is_single_full_object() ? 
+            TransformationType::Instance_Relative_Independent:
+            TransformationType::Local_Relative_Independent;
         selection.rotate(Vec3d(0., 0., relative_angle), transformation_type);    
     };
     selection_transform(selection, selection_rotate_fnc);
@@ -438,6 +438,13 @@ void do_local_z_move(GLCanvas3D &canvas, double relative_move) {
     canvas.do_move(snapshot_name);
 }
 
+TransformationType get_drag_transformation_type(const Selection &selection)
+{
+    assert(selection.volumes_count() == 1);
+    return selection.is_single_full_object() ? 
+        TransformationType::Instance_Relative_Joint : 
+        TransformationType::Local_Relative_Joint;
+}
 } // namespace Slic3r::GUI
 
 // private implementation
diff --git a/src/slic3r/GUI/SurfaceDrag.hpp b/src/slic3r/GUI/SurfaceDrag.hpp
index 6bc3c523ed..aaf506582d 100644
--- a/src/slic3r/GUI/SurfaceDrag.hpp
+++ b/src/slic3r/GUI/SurfaceDrag.hpp
@@ -15,6 +15,7 @@ class ModelVolume;
 namespace Slic3r::GUI {
 class GLCanvas3D;
 class Selection;
+class TransformationType;
 struct Camera;
 
 // Data for drag&drop over surface with mouse
@@ -148,5 +149,12 @@ void do_local_z_rotate(GLCanvas3D &canvas, double relative_angle);
 /// <param name="relative_move">Relative move along emboss direction</param>
 void do_local_z_move(GLCanvas3D &canvas, double relative_move);
 
+/// <summary>
+/// 
+/// </summary>
+/// <param name="selection"></param>
+/// <returns></returns>
+TransformationType get_drag_transformation_type(const Selection &selection);
+
 } // namespace Slic3r::GUI
 #endif // slic3r_SurfaceDrag_hpp_
\ No newline at end of file