diff --git a/notmuch.el b/notmuch.el
index 014d15bc..ed1b363b 100644
--- a/notmuch.el
+++ b/notmuch.el
@@ -53,6 +53,7 @@
     (define-key map (kbd "DEL") 'notmuch-show-rewind)
     (define-key map " " 'notmuch-show-advance-marking-read-and-archiving)
     (define-key map "|" 'notmuch-show-pipe-message)
+    (define-key map "?" 'describe-mode)
     map)
   "Keymap for \"notmuch show\" buffers.")
 (fset 'notmuch-show-mode-map notmuch-show-mode-map)
@@ -698,6 +699,7 @@ thread from that buffer can be show when done with this one)."
     (define-key map "\M->" 'notmuch-search-goto-last-thread)
     (define-key map " " 'notmuch-search-scroll-up)
     (define-key map (kbd "<DEL>") 'notmuch-search-scroll-down)
+    (define-key map "?" 'describe-mode)
     map)
   "Keymap for \"notmuch search\" buffers.")
 (fset 'notmuch-search-mode-map notmuch-search-mode-map)