Index: html-filter.scm
==================================================================
--- html-filter.scm
+++ html-filter.scm
@@ -166,11 +166,12 @@
 		  result
 		  (loop (car tail)(cdr tail) result))
 	      (let* ((key (substring head 0 2))
 		     (rem (substring head 2 (string-length head)))
 		     (num (string->number key 16))
-		     (ch  (if (exact? num)
+		     (ch  (if (and (number? num)
+                                   (exact? num))
 			      (integer->char num)
 			      #f)) ;; this is an error. I will probably regret this some day
 		     (chstr  (if ch (make-string 1 ch) ""))
 		     (newres (if ch
 				 (string-append result chstr rem)