diff --git a/src/slic3r/GUI/GUI_ObjectList.cpp b/src/slic3r/GUI/GUI_ObjectList.cpp
index c11ed66ab..d44db72b1 100644
--- a/src/slic3r/GUI/GUI_ObjectList.cpp
+++ b/src/slic3r/GUI/GUI_ObjectList.cpp
@@ -350,7 +350,7 @@ void ObjectList::get_selection_indexes(std::vector<int>& obj_idxs, std::vector<i
     else {
         for (wxDataViewItem item : sels) {
             const ItemType type = m_objects_model->GetItemType(item);
-            assert(type & itObject | itInstance | itInstanceRoot);
+            assert(type & (itObject | itInstance | itInstanceRoot));
 
             obj_idxs.emplace_back(type & itObject ? m_objects_model->GetIdByItem(item) :
                                   m_objects_model->GetIdByItem(m_objects_model->GetTopParent(item)));