diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index 8b38dabbe..a5b6866ab 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -3180,7 +3180,9 @@ void GLCanvas3D::on_mouse(wxMouseEvent& evt)
                 return;
         }
 
-        if (evt.LeftDown() && (evt.ShiftDown() || evt.AltDown()) && m_picking_enabled) {
+        // BBS: define Alt key to enable volume selection mode
+        m_selection.set_volume_selection_mode(evt.AltDown() ? Selection::Volume : Selection::Instance);
+        if (evt.LeftDown() && evt.ShiftDown() && m_picking_enabled) {
             if (m_gizmos.get_current_type() != GLGizmosManager::SlaSupports
              && m_gizmos.get_current_type() != GLGizmosManager::FdmSupports
              && m_gizmos.get_current_type() != GLGizmosManager::Seam
diff --git a/src/slic3r/GUI/GUI_Preview.cpp b/src/slic3r/GUI/GUI_Preview.cpp
index 374894a50..d9db9e0f3 100644
--- a/src/slic3r/GUI/GUI_Preview.cpp
+++ b/src/slic3r/GUI/GUI_Preview.cpp
@@ -766,6 +766,7 @@ bool AssembleView::init(wxWindow* parent, Bed3D& bed, Model* model, DynamicPrint
 
     // BBS: set volume_selection_mode to Volume
     m_canvas->get_selection().set_volume_selection_mode(Selection::Volume);
+    m_canvas->get_selection().lock_volume_selection_mode();
 
     wxBoxSizer* main_sizer = new wxBoxSizer(wxVERTICAL);
     main_sizer->Add(m_canvas_widget, 1, wxALL | wxEXPAND, 0);
diff --git a/src/slic3r/GUI/Selection.hpp b/src/slic3r/GUI/Selection.hpp
index 5c24160f9..96a98e5ab 100644
--- a/src/slic3r/GUI/Selection.hpp
+++ b/src/slic3r/GUI/Selection.hpp
@@ -226,6 +226,7 @@ private:
 
     // BBS
     EMode m_volume_selection_mode{ Instance };
+    bool m_volume_selection_locked { false };
 
 public:
     Selection();
@@ -343,7 +344,10 @@ public:
     void translate(unsigned int object_idx, unsigned int instance_idx, const Vec3d& displacement);
     //BBS: add partplate related logic
     void notify_instance_update(int object_idx, int instance_idx);
-    void set_volume_selection_mode(EMode mode) { m_volume_selection_mode = mode; }
+    // BBS
+    void set_volume_selection_mode(EMode mode) { if (!m_volume_selection_locked) m_volume_selection_mode = mode; }
+    void lock_volume_selection_mode() { m_volume_selection_locked = true; }
+    void unlock_volume_selection_mode() { m_volume_selection_locked = false; }
 
     void erase();