diff --git a/src/slic3r/GUI/MainFrame.cpp b/src/slic3r/GUI/MainFrame.cpp
index 8c54e10f87..e7065cb13a 100644
--- a/src/slic3r/GUI/MainFrame.cpp
+++ b/src/slic3r/GUI/MainFrame.cpp
@@ -544,9 +544,12 @@ void MainFrame::init_tabpanel()
 
     m_tabpanel->Bind(wxEVT_NOTEBOOK_PAGE_CHANGED, [this](wxBookCtrlEvent& e) {
 #if ENABLE_VALIDATE_CUSTOM_GCODE
-        Tab* old_tab = dynamic_cast<Tab*>(m_tabpanel->GetPage(e.GetOldSelection()));
-        if (old_tab)
-            old_tab->validate_custom_gcodes();
+        if (int old_selection = e.GetOldSelection();
+            old_selection != wxNOT_FOUND && old_selection < m_tabpanel->GetPageCount()) {
+            Tab* old_tab = dynamic_cast<Tab*>(m_tabpanel->GetPage(old_selection));
+            if (old_tab)
+                old_tab->validate_custom_gcodes();
+        }
 #endif // ENABLE_VALIDATE_CUSTOM_GCODE
 
         wxWindow* panel = m_tabpanel->GetCurrentPage();