diff --git a/lens.lisp b/lens.lisp
index 21fca6e..4bbda76 100644
--- a/lens.lisp
+++ b/lens.lisp
@@ -225,9 +225,10 @@
 
 (defun transform-elt (elt fun)
   (lambda (it)
-    (append (subseq it 0 elt)
-            (list (funcall fun (nth elt it)))
-            (subseq it (1+ elt)))))
+    (concatenate (type-of it)
+                 (subseq it 0 elt)
+                 (list (funcall fun (elt it elt)))
+                 (subseq it (1+ elt)))))
 
 (defun key-transform (fun key-get key-set)
   (lambda (it)
diff --git a/t/lens.lisp b/t/lens.lisp
index 099f10e..953dc15 100644
--- a/t/lens.lisp
+++ b/t/lens.lisp
@@ -259,3 +259,18 @@
   (5am:is (equalp #(1 2 3)
                   (funcall (data-lens:over '1+ :result-type 'vector)
                            #(0 1 2)))))
+
+(5am:def-test transform-elt (:suite :data-lens.lens :depends-on (and functionalize))
+  (5am:is (equal '(1 1 2)
+                 (funcall (data-lens:transform-elt 0 '1+)
+                          '(0 1 2))))
+  (5am:is (equal '(0 2 2)
+                 (funcall (data-lens:transform-elt 1 '1+)
+                          '(0 1 2))))
+  (5am:is (equalp #(0 1 3)
+                  (funcall (data-lens:transform-elt 2 '1+)
+                           (vector 0 1 2))))
+  (5am:is (equal "Abc"
+                 (funcall (data-lens:transform-elt 0 'char-upcase)
+                          "abc")))
+  )