diff --git a/benchs/raytracer/dune b/benchs/raytracer/dune
new file mode 100644
index 00000000..b821229d
--- /dev/null
+++ b/benchs/raytracer/dune
@@ -0,0 +1,4 @@
+
+(executable
+  (name raytracer)
+  (flags :standard -warn-error -a+8))
diff --git a/benchs/raytracer/raytracer.ml b/benchs/raytracer/raytracer.ml
index f8736343..988eee78 100644
--- a/benchs/raytracer/raytracer.ml
+++ b/benchs/raytracer/raytracer.ml
@@ -1,4 +1,3 @@
-open Core
 open Printf
 open Vec3
 open Ray
@@ -120,9 +119,8 @@ let hit_sphere sphere ray (tmin, tmax) =
   else None
 
 let rec hit_world world ray (tmin, tmax) =
-  List.fold world
-    ~init: None
-    ~f: (fun acc h ->
+  List.fold_left 
+    (fun acc h ->
         let prev_rec = match acc with
             None -> { t = tmax;
                       p = Vec3.of_floats (-1., -1., -1.);
@@ -131,7 +129,7 @@ let rec hit_world world ray (tmin, tmax) =
           | Some(r) -> r in
         match (hit h ray (tmin, prev_rec.t)) with
           Some(r) -> Some r
-        | None -> acc)
+        | None -> acc) None world
 
 and hit h ray (tmin, tmax) =
   match h with
@@ -175,7 +173,7 @@ let write_to_file filename =
   let nx = 400 in
   let ny = 200 in
   let ns = 150 in               (* samples per pixel *)
-  let oc = Out_channel.create filename in
+  let oc = open_out filename in
   fprintf oc "P3\n";
   fprintf oc "%d\n" nx;
   fprintf oc "%d\n"  ny;