diff --git a/lens/base/contract.rkt b/lens/base/contract.rkt
index 52c38ac..aae3889 100644
--- a/lens/base/contract.rkt
+++ b/lens/base/contract.rkt
@@ -3,6 +3,7 @@
 (provide lens/c)
 
 (require racket/contract/base
+         unstable/contract
          "gen-lens.rkt"
          )
 (module+ test
@@ -13,10 +14,12 @@
            ))
 
 (define (lens/c target/c view/c)
-  (gen-lens/c
-   [lens-view (or/c #f [lens? target/c . -> . view/c])]
-   [lens-set (or/c #f [lens? target/c view/c . -> . target/c])]
-   [focus-lens (or/c #f [lens? target/c . -> . (values view/c [view/c . -> . target/c])])]))
+  (rename-contract
+   (gen-lens/c
+    [lens-view (or/c #f [lens? target/c . -> . view/c])]
+    [lens-set (or/c #f [lens? target/c view/c . -> . target/c])]
+    [focus-lens (or/c #f [lens? target/c . -> . (values view/c [view/c . -> . target/c])])])
+   `(lens/c ,(contract-name target/c) ,(contract-name view/c))))
 
 (module+ test
   (check-exn exn:fail:contract?
diff --git a/lens/util/immutable.rkt b/lens/util/immutable.rkt
index 9f82d91..781444f 100644
--- a/lens/util/immutable.rkt
+++ b/lens/util/immutable.rkt
@@ -2,6 +2,8 @@
 
 (provide (all-defined-out))
 
+(require racket/vector)
+
 ;; The immutable? predicate only works for strings, byte-strings, vectors, hash-tables, and boxes.
 
 (define (immutable-string? v)
@@ -31,3 +33,6 @@
 (define (build-immutable-vector n f)
   (vector->immutable-vector (build-vector n f)))
 
+(define (immutable-vector-map f v)
+  (vector->immutable-vector (vector-map f v)))
+
diff --git a/unstable/lens/mapper.rkt b/unstable/lens/mapper.rkt
index c74cb58..12ade24 100644
--- a/unstable/lens/mapper.rkt
+++ b/unstable/lens/mapper.rkt
@@ -49,6 +49,7 @@
                 '#(a c e))
   (check-equal? (lens-set (vector-mapper-lens first-lens) '#((a b) (c d) (e f)) '#(1 2 3))
                 '#((1 b) (2 d) (3 f)))
-  (check-equal? (lens-transform (vector-mapper-lens first-lens) '#((a b) (c d) (e f)) (vector-map symbol->string _))
+  (check-equal? (lens-transform (vector-mapper-lens first-lens) '#((a b) (c d) (e f))
+                                (immutable-vector-map symbol->string _))
                 '#(("a" b) ("c" d) ("e" f)))
   )
diff --git a/unstable/lens/mapper.scrbl b/unstable/lens/mapper.scrbl
index e6e7933..7e0a2ba 100644
--- a/unstable/lens/mapper.scrbl
+++ b/unstable/lens/mapper.scrbl
@@ -19,5 +19,6 @@ Creates a lens that maps @racket[lens] over a target vector with @racket[vector-
 @lenses-unstable-examples[
   (lens-view (vector-mapper-lens first-lens) '#((a b) (c d) (e f)))
   (lens-set (vector-mapper-lens first-lens) '#((a b) (c d) (e f)) '#(1 2 3))
-  (lens-transform (vector-mapper-lens first-lens) '#((a b) (c d) (e f)) (λ (xs) (vector-map symbol->string xs)))
+  (lens-transform (vector-mapper-lens first-lens) '#((a b) (c d) (e f))
+                  (λ (xs) (vector->immutable-vector (vector-map symbol->string xs))))
 ]}