diff --git a/src/libslic3r/Print.cpp b/src/libslic3r/Print.cpp
index 6eb2b068e..cb72ac229 100644
--- a/src/libslic3r/Print.cpp
+++ b/src/libslic3r/Print.cpp
@@ -341,7 +341,7 @@ std::vector<unsigned int> Print::extruders(bool conside_custom_gcode) const
         for (auto plate_data : m_model.plates_custom_gcodes) {
             for (auto item : plate_data.second.gcodes) {
                 if (item.type == CustomGCode::Type::ToolChange)
-                    extruders.push_back((unsigned int)item.extruder);
+                    extruders.push_back((unsigned int)(item.extruder - 1));
             }
         }
     }
diff --git a/src/slic3r/GUI/GCodeViewer.cpp b/src/slic3r/GUI/GCodeViewer.cpp
index 96b7fcb75..121e85083 100644
--- a/src/slic3r/GUI/GCodeViewer.cpp
+++ b/src/slic3r/GUI/GCodeViewer.cpp
@@ -3176,19 +3176,8 @@ void GCodeViewer::load_shells(const Print& print, bool initialized, bool force_p
     }
 
     if (wxGetApp().preset_bundle->printers.get_edited_preset().printer_technology() == ptFFF) {
-        // BBS
-        // adds wipe tower's volume
-        std::vector<int> print_extruders;
-        for (auto print_obj : print.objects()) {
-            ModelObject* mo = print_obj->model_object();
-            for (ModelVolume* mv : mo->volumes) {
-                std::vector<int> volume_extruders = mv->get_extruders();
-                print_extruders.insert(print_extruders.end(), volume_extruders.begin(), volume_extruders.end());
-            }
-        }
-        std::sort(print_extruders.begin(), print_extruders.end());
-        auto it_end = std::unique(print_extruders.begin(), print_extruders.end());
-        print_extruders.resize(std::distance(print_extruders.begin(), it_end));
+        // BBS: adds wipe tower's volume
+        std::vector<unsigned int> print_extruders = print.extruders(true);
         int extruders_count = print_extruders.size();
 
         const double max_z = print.objects()[0]->model_object()->get_model()->bounding_box().max(2);