diff --git a/tests/bench_conv.ml b/tests/bench_conv.ml
index 854288e6..9c84daba 100644
--- a/tests/bench_conv.ml
+++ b/tests/bench_conv.ml
@@ -40,6 +40,39 @@ let bench_point_list x =
     ] in
   Benchmark.tabulate res
 
+(* conversion back from json *)
+let rec point_of_json_manual (j:Conv.Json.t) =
+  let module P = Point in
+  match j with
+  | `Assoc l ->
+      let x = List.assoc "x" l in
+      let y = List.assoc "y" l in
+      let color = List.assoc "color" l in
+      let prev = List.assoc "prev" l in
+      let prev = match prev with
+        | `String "none" -> None
+        | `List [`String "some"; p'] -> Some (point_of_json_manual p')
+        | _ -> failwith "expected point"
+      in
+      begin match x, y, color with
+      | `Int x, `Int y, `String color -> P.({x;y;color;prev;})
+      | _ -> failwith "expected point"
+      end
+  | _ -> failwith "expected point"
+
+let points_of_json_manual = function
+  | `List l -> List.map point_of_json_manual l
+  | _ -> failwith "expected list of points"
+
+let points_of_json_conv =
+  Conv.from Conv.Json.source (Conv.Sink.list_ Point.sink)
+
+let bench_point_list_back l =
+  let res = Benchmark.throughputN 5 
+    [ "conv", points_of_json_conv, l
+    ; "manual", points_of_json_manual, l
+    ] in
+  Benchmark.tabulate res
 
 let () =
   Printf.printf "list of 5 elements...\n";
@@ -52,4 +85,9 @@ let () =
   let l = Gen.(repeat Point.p |> take 10 |> to_rev_list) in
   Printf.printf "list of %d points...\n" (List.length l);
   bench_point_list l;
+
+  (* convert back from json *)
+  let l' = conv_list_point_to_json l in
+  Printf.printf "from JSON...\n";
+  bench_point_list_back l';
   ()