diff --git a/scsh/rx/parse.scm b/scsh/rx/parse.scm
index b7881c4..0d087fa 100644
--- a/scsh/rx/parse.scm
+++ b/scsh/rx/parse.scm
@@ -114,6 +114,9 @@
 ;;; returns a regexp value. R and C are low-level macro rename and compare
 ;;; functions.
 
+(define *control-charset* (char-set-delete char-set:iso-control
+					   (ascii->char 0)))
+
 (define (parse-sre/context sre case-sensitive? cset? r c)
   (let ((%bos (r 'bos))		(%eos (r 'eos))
 	(%bol (r 'bol))		(%eol (r 'eol))
@@ -288,7 +291,7 @@
 		     ((hygn-memq? '(blank))			char-set:blank)
 		     ((hygn-memq? '(whitespace space white))	char-set:whitespace)
 		     ((hygn-memq? '(printing print))		char-set:printing)
-		     ((hygn-memq? '(control cntrl))		char-set:iso-control)
+		     ((hygn-memq? '(control cntrl))		*control-charset*)
 		     ((hygn-memq? '(hex-digit xdigit hex))	char-set:hex-digit)
 		     ((hygn-memq? '(ascii))			char-set:ascii)
 		     (else (error "Illegal regular expression" sre)))))
@@ -465,6 +468,7 @@
 		    (switch char-set= cs
 		      ((char-set:punctuation)	punct)
 		      ((char-set:iso-control)	ctl)
+		      ((*control-charset*)	ctl)
 		      (else #f))))))))