diff --git a/bypy/windows/site.py b/bypy/windows/site.py
index ef9b55634f..952c23bbbb 100644
--- a/bypy/windows/site.py
+++ b/bypy/windows/site.py
@@ -88,7 +88,7 @@ if __name__ == '__main__':
     try:
         main()
     except Exception:
-        if sys.gui_app:
+        if sys.gui_app and sys.excepthook == sys.__excepthook__:
             import traceback
             import calibre_os_module
             calibre_os_module.gui_error_message(