diff -Naur chicken-1.45/extras.scm chicken-1.45-alejo/extras.scm
--- chicken-1.45/extras.scm	2004-04-26 14:23:02.000000000 -0500
+++ chicken-1.45-alejo/extras.scm	2004-05-17 17:27:56.000000000 -0500
@@ -384,6 +384,7 @@
     (lambda (s . more)
       (##sys#check-string s 'write-string)
       (let-optionals more ([n #f] [port ##sys#standard-output])
+	(when n (##sys#check-exact n 'write-string))
 	(display 
 	 (if (and n (fx< n (##sys#size s)))
 	     (##sys#substring s 0 n)