diff --git a/emacs/notmuch-tree.el b/emacs/notmuch-tree.el
index 1ab0810d..220c010d 100644
--- a/emacs/notmuch-tree.el
+++ b/emacs/notmuch-tree.el
@@ -258,6 +258,7 @@ FUNC."
     (define-key map (kbd "<backtab>")  (notmuch-tree-to-message-pane #'notmuch-show-previous-button))
     (define-key map (kbd "TAB") (notmuch-tree-to-message-pane #'notmuch-show-next-button))
     (define-key map "e" (notmuch-tree-to-message-pane #'notmuch-tree-button-activate))
+    (define-key map "$" (notmuch-tree-to-message-pane #'notmuch-show-toggle-process-crypto))
 
     ;; bindings from show (or elsewhere) but we close the message pane first.
     (define-key map "f" (notmuch-tree-close-message-pane-and #'notmuch-show-forward-message))