'notmuch-interactive-region
   "notmuch 0.29")
 
+(defun notmuch--inline-override-types ()
+  "Override mm-inline-override-types to stop application/*
+parts from being displayed unless the user has customized
+it themselves."
+  (if (equal mm-inline-override-types
+            (eval (car (get 'mm-inline-override-types 'standard-value))))
+      (cons "application/.*" mm-inline-override-types)
+    mm-inline-override-types))
 ;;; _
 
 (provide 'notmuch-lib)
 
   (let ((buffer-name (generate-new-buffer-name
                      (or buffer-name
                          (concat "*notmuch-" thread-id "*"))))
-       ;; We override mm-inline-override-types to stop application/*
-       ;; parts from being displayed unless the user has customized
-       ;; it themselves.
-       (mm-inline-override-types
-        (if (equal mm-inline-override-types
-                   (eval (car (get 'mm-inline-override-types 'standard-value))))
-            (cons "application/*" mm-inline-override-types)
-          mm-inline-override-types)))
+       (mm-inline-override-types (notmuch--inline-override-types)))
+
     (pop-to-buffer-same-window (get-buffer-create buffer-name))
     ;; No need to track undo information for this buffer.
     (setq buffer-undo-list t)