diff --git a/lens/list/car-cdr.rkt b/lens/list/car-cdr.rkt
index 91d6495..4016316 100644
--- a/lens/list/car-cdr.rkt
+++ b/lens/list/car-cdr.rkt
@@ -1,6 +1,8 @@
-#lang racket/base
+#lang racket
 
-(provide car-lens cdr-lens)
+(provide
+ (contract-out [car-lens lens?]
+               [cdr-lens lens?]))
 
 (require "../base/main.rkt")