diff --git a/lisp/apropos.el b/lisp/apropos.el

index 3c1a413..a2bfee9 100644

--- a/lisp/apropos.el

+++ b/lisp/apropos.el

@@ -505,7 +505,8 @@ apropos-user-option

 ;;;###autoload

 (defun apropos-variable (pattern &optional do-not-all)

   "Show variables that match PATTERN.

-When DO-NOT-ALL is non-nil, show user options only, i.e. behave

+With the optional argument DO-NOT-ALL non-nil (or when called interactively with

+the prefix \\[universal-argument]), show user options only, i.e. behave

 like `apropos-user-option'."

   (interactive (list (apropos-read-pattern

       (if current-prefix-arg "user option" "variable"))