diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index 18bc08d27..28474cac9 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -4336,14 +4336,14 @@ void Plater::set_number_of_copies(/*size_t num*/)
 
     ModelObject* model_object = p->model.objects[obj_idx];
 
-    const auto num = wxGetNumberFromUser( " ", _("Enter the number of copies:"),
+    const int num = wxGetNumberFromUser( " ", _("Enter the number of copies:"),
                                     _("Copies of the selected object"), model_object->instances.size(), 0, 1000, this );
     if (num < 0)
         return;
 
     Plater::TakeSnapshot snapshot(this, wxString::Format(_(L("Set numbers of copies to %d")), num));
 
-    int diff = (int)num - (int)model_object->instances.size();
+    int diff = num - (int)model_object->instances.size();
     if (diff > 0)
         increase_instances(diff);
     else if (diff < 0)