diff --git a/lisp/international/mule-diag.el b/lisp/international/mule-diag.el
index 472529ffc05..dcdcafcea77 100644
--- a/lisp/international/mule-diag.el
+++ b/lisp/international/mule-diag.el
@@ -677,7 +677,8 @@ Priority order for recognizing coding systems when reading files:\n")
 			(princ (cdr (car alist)))
 			(princ "\n")
 			(setq alist (cdr alist)))))))
-	(funcall func "File I/O" file-coding-system-alist)
+	(funcall func "File I/O" (append auto-coding-alist
+                                         file-coding-system-alist))
 	(funcall func "Process I/O" process-coding-system-alist)
 	(funcall func "Network I/O" network-coding-system-alist))
       (help-mode))))