diff --git a/csi.scm b/csi.scm
index 5f424f6..dcf512e 100644
--- a/csi.scm
+++ b/csi.scm
@@ -26,7 +26,7 @@
 
 
 (declare
-  (uses chicken-syntax srfi-69 ports extras)
+  (uses chicken-syntax srfi-69 srfi-1 ports extras)
   (usual-integrations)
   (disable-interrupts)
   (disable-warning var)
@@ -525,6 +525,15 @@ EOF
 		    (lambda ()
 		      (write (cadr plist) out) ) )
 		   (newline out) ) ) ) ]
+	    [(circular-list? x) (begin
+				  (fprintf out "circular list: ")
+				  (let loop-print ((x x)
+						   (parsed '()))
+				    (if (not (memq (car x) parsed))
+					(begin
+					  (fprintf out "~S -> " (car x))
+					  (loop-print (cdr x) (cons (car x) parsed)))
+					(fprintf out " ~S (circle)~%" (car (memq (car x) parsed))))))]
 	    [(list? x) (descseq "list" length list-ref 0)]
 	    [(pair? x) (fprintf out "pair with car ~S and cdr ~S~%" (car x) (cdr x))]
 	    [(procedure? x)