diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index 812e28268c2..4e3b18a327b 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -361,6 +361,11 @@ python-mode-map
   ;; Utilities
   "<remap> <complete-symbol>" #'completion-at-point)
 
+;; Define this so invoking menu-bar-open in a python-mode buffer does
+;; not cause a void-variable error when subword-mode is not loaded,
+;; menu-bar-mode is disabled and debug-on-error is enabled (bug#xxx).
+(defvar subword-mode nil)
+
 (easy-menu-define python-menu python-mode-map
   "Menu used for ´python-mode'."
   '("Python"