diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index 43408d98..aa9cceed 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -1124,7 +1124,7 @@ This includes:
 Refreshes the current view, observing changes in display
 preferences. If RETAIN-STATE is non-nil then the state of the
 buffer is stored and re-applied after the refresh."
-  (interactive)
+  (interactive "P")
   (let ((inhibit-read-only t)
 	state)
     (if retain-state