diff --git a/lisp/ielm.el b/lisp/ielm.el
index b4ad69e4c7..4bb6e752e8 100644
--- a/lisp/ielm.el
+++ b/lisp/ielm.el
@@ -546,6 +546,8 @@ inferior-emacs-lisp-mode
   (set (make-local-variable 'paragraph-start) comint-prompt-regexp)
   (setq comint-input-sender 'ielm-input-sender)
   (setq comint-process-echoes nil)
+  (unless (string-match-p " " comint-file-name-chars)
+    (setq comint-file-name-chars (concat " " comint-file-name-chars)))
   (set (make-local-variable 'completion-at-point-functions)
        '(comint-replace-by-expanded-history
          ielm-complete-filename elisp-completion-at-point))