diff --git a/lisp/progmodes/octave.el b/lisp/progmodes/octave.el
index 1803ea62c13..f128441a54e 100644
--- a/lisp/progmodes/octave.el
+++ b/lisp/progmodes/octave.el
@@ -1747,7 +1747,7 @@ sentence."
           (insert "\nRetry with ")
           (insert-text-button "'-all'"
                               'follow-link t
-                              'action #'(lambda (b)
+                              'action #'(lambda (_b)
                                           (octave-lookfor str '-all)))
           (insert ".\n"))
         (octave-help-mode)))))