Fix read-buffer-function type.

diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index c2a3a32e218514d7752b04a16989f6f9801410c2..2709588840e0102a6eb17a6fd79e4fb07dcd7f54 100644 (file)
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -179,7 +179,7 @@
              "21.1")
             (minibuffer-auto-raise minibuffer boolean)
             ;; options property set at end
-            (read-buffer-function minibuffer (choice nil function))
+            (read-buffer-function minibuffer (choice (const nil) function))
             ;; msdos.c
             (dos-unsupported-char-glyph display integer)
             ;; process.c