diff --git a/collects/parser-tools/private-lex/re.ss b/collects/parser-tools/private-lex/re.ss
index eccce9a..3e1eea0 100644
--- a/collects/parser-tools/private-lex/re.ss
+++ b/collects/parser-tools/private-lex/re.ss
@@ -11,7 +11,7 @@
            orR-res andR-res negR-re
            re-nullable? re-index)
   
-  (define max-char-num #x7FFFFFFF)
+  (define max-char-num #x10FFFF)
   
   ;; get-index : -> nat
   (define get-index (make-counter))
@@ -384,4 +384,4 @@
                (isc (is:make-range 0)))
               )
   
-  )
\ No newline at end of file
+  )