diff --git a/lisp/international/quail.el b/lisp/international/quail.el
index aec2358fdaa..7cedcbf665a 100644
--- a/lisp/international/quail.el
+++ b/lisp/international/quail.el
@@ -2772,6 +2772,8 @@ If CHAR is an ASCII character and can be input by typing itself, return t."
   (interactive)
   (or current-input-method
       (error "No input method is activated"))
+  (or (assoc current-input-method quail-package-alist)
+      (error "The current input method is not using Quail."))
   (let* ((char (following-char))
 	 (key-list (quail-find-key char)))
     (cond ((consp key-list)