--- imap.el~	2002-08-12 22:00:26 +0000
+++ imap.el	2002-08-26 23:44:57 +0000
@@ -414,7 +414,8 @@
 
 (defsubst imap-disable-multibyte ()
   "Enable multibyte in the current buffer."
-  (when (fboundp 'set-buffer-multibyte)
+  (when (and (fboundp 'set-buffer-multibyte)
+	     (subrp (symbol-function 'set-buffer-multibyte)))
     (set-buffer-multibyte nil)))
 
 (defun imap-read-passwd (prompt &rest args)