diff --git a/lisp/subr.el b/lisp/subr.el
index a3d6554e354..90588a90046 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -512,6 +512,8 @@ as returned by the `event-start' and `event-end' functions."
 (defalias 'define-function 'defalias)
 
 (defun sref (string byte-index)
+  "Obsolete function returning a characater in STRING at BYTE-INDEX.
+Please convert your programs to use `aref' witha character-base index."
   (let ((byte 0) (char 0))
     (while (< byte byte-index)
       (setq byte (+ byte (char-bytes (aref string byte)))))