diff --git a/lisp/progmodes/js.el b/lisp/progmodes/js.el
index a94a2fe134e..6e18e30517a 100644
--- a/lisp/progmodes/js.el
+++ b/lisp/progmodes/js.el
@@ -477,6 +477,7 @@ This applies to function movement, marking, and so on."
   "Align continuation of non-empty ([{ lines in `js-mode'."
   :version "26.1"
   :type 'boolean
+  :safe 'booleanp
   :group 'js)
 
 (defcustom js-comment-lineup-func #'c-lineup-C-comments