...

src/calibre/gui2/main.py

@@ -303,7 +303,7 @@ def run_gui(opts, args, actions, listener, app, gui_debug=None):
                 runner.main.system_tray_icon.hide()
             except:
                 pass
-    if runner.main.gui_debug is not None:
+    if getattr(runner.main, 'gui_debug', None) is not None:
         e = sys.executable if getattr(sys, 'frozen', False) else sys.argv[0]
         import subprocess
         creationflags = 0