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diff --git a/FAQ b/FAQ
index 89cbcac3..91d12cf5 100644
--- a/FAQ
+++ b/FAQ
@@ -52,6 +52,19 @@ A. Once X-Symbol is picked up by Emacs (e.g. is working for TeX),
 
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+Q. I notice that editing Isabelle files in Proof General with XEmacs
+   21.4 is very slow.  Can this be fixed?
+
+A. You could consider adding the following line to your init file:
+
+      (setq lookup-syntax-properties nil)
+
+   This hack bypasses some very slow code in the font-lock system, but
+   it also disables some syntax-related features, so use with care.
+
+-----------------------------------------------------------------
+
+
 Q. I'm afraid I got stuck very early on.  I sent the following line:
 
       by (swap_res_tac [psubsetI] 1;