diff --git a/test_wycheproof/test.ml b/test_wycheproof/test.ml
index 53971be..4034a8b 100644
--- a/test_wycheproof/test.ml
+++ b/test_wycheproof/test.ml
@@ -12,68 +12,85 @@ let strip_prefix s ~prefix =
       Some (Str.string_after s prefix_len)
     else None
 
-let rec strip_prefixes s ~prefixes =
-  match prefixes with
-  | [] ->
-      None
-  | prefix :: prefixes -> (
-    match strip_prefix s ~prefix with
-    | Some _ as r ->
-        r
-    | None ->
-        strip_prefixes s ~prefixes )
-
-let strip_asn1 =
-  let prefixes =
-    List.map Hex.to_string
-      [`Hex "3059301306072a8648ce3d020106082a8648ce3d030107034200"]
+let result_of_option ~msg = function
+  | None ->
+      Error msg
+  | Some x ->
+      Ok x
+
+let strip_asn1 s =
+  let prefix =
+    Hex.to_string
+      (`Hex "3059301306072a8648ce3d020106082a8648ce3d030107034200")
   in
-  strip_prefixes ~prefixes
+  result_of_option ~msg:"unknown ASN1 prefix" (strip_prefix ~prefix s)
+
+let ( >>= ) xr f =
+  match xr with
+  | Error _ as e ->
+      e
+  | Ok x ->
+      f x
 
 let parse_point s =
-  match strip_asn1 s with
-  | Some payload ->
-      Fiat_p256.point_of_hex (Hex.of_string payload)
-  | None ->
-      None
-
-let parse_scalar s = Fiat_p256.scalar_of_hex (Hex.of_string s)
-
-let test_valid ~private_ ~public ~expected () =
-  match (parse_point public, parse_scalar private_) with
-  | Some point, Some scalar ->
-      let got = Cstruct.to_string (Fiat_p256.dh ~scalar ~point) in
-      Alcotest.check hex "should be equal" expected got
-  | _ ->
-      failwith "cannot parse test case"
-
-(*
-let test_invalid ~private_ ~public () =
-  Alcotest.check_raises "should raise" Unverified_api.Error (fun () ->
-      let scalar = Unverified_api.parse_scalar private_ in
-      let point = Unverified_api.parse_point public in
-      ignore (Unverified_api.dh scalar point) )
-   *)
-
-let make_test {tcId; comment; private_; public; shared; result; flags; _} =
-  let name = Printf.sprintf "%d - %s" tcId comment in
-  let ignored_flags = [invalid_asn; compressed_point; unnamed_curve] in
-  match result with
+  strip_asn1 s
+  >>= fun payload ->
+  result_of_option ~msg:"cannot parse point"
+    (Fiat_p256.point_of_hex (Hex.of_string payload))
+
+let parse_scalar s =
+  result_of_option ~msg:"cannot parse scalar"
+    (Fiat_p256.scalar_of_hex (Hex.of_string s))
+
+type test =
+  { name : string
+  ; point : Fiat_p256.point
+  ; scalar : Fiat_p256.scalar
+  ; expected : string }
+
+let interpret_test {name; point; scalar; expected} =
+  let run () =
+    let got = Cstruct.to_string (Fiat_p256.dh ~scalar ~point) in
+    Alcotest.check hex __LOC__ expected got
+  in
+  (name, `Quick, run)
+
+type strategy =
+  | Test of test
+  | Skip
+
+let test_name test = Printf.sprintf "%d - %s" test.tcId test.comment
+
+let make_test test =
+  let ignored_flags = ["InvalidAsn"; "CompressedPoint"; "UnnamedCurve"] in
+  match test.result with
   | _
-    when List.exists
-           (fun ignored_flag -> List.mem ignored_flag flags)
-           ignored_flags ->
-      []
+    when has_ignored_flag test ~ignored_flags ->
+      Ok Skip
+  | Invalid ->
+      Ok Skip
   | Valid
    |Acceptable ->
-      [(name, `Quick, test_valid ~private_ ~public ~expected:shared)]
-  | Invalid ->
+      parse_point test.public
+      >>= fun point ->
+      parse_scalar test.private_
+      >>= fun scalar ->
+      let name = test_name test in
+      Ok (Test {name; point; scalar; expected = test.shared})
+
+let concat_map f l = List.map f l |> List.concat
+
+let to_tests x =
+  match make_test x with
+  | Ok (Test t) ->
+      [interpret_test t]
+  | Ok Skip ->
       []
+  | Error e ->
+      failwith e
 
 let tests =
   let data = load_file_exn "ecdh_secp256r1_test.json" in
-  data.testGroups
-  |> List.map (fun group -> List.map make_test group.tests |> List.concat)
-  |> List.concat
+  concat_map (fun group -> concat_map to_tests group.tests) data.testGroups
 
 let () = Alcotest.run "Wycheproof-hacl-p256" [("test vectors", tests)]
diff --git a/wycheproof/wycheproof.ml b/wycheproof/wycheproof.ml
index 30e6621..66edcf1 100644
--- a/wycheproof/wycheproof.ml
+++ b/wycheproof/wycheproof.ml
@@ -34,57 +34,6 @@ let test_result_of_yojson = function
   | _ ->
       Error "test_result"
 
-type flag =
-  | Twist
-  | LowOrderPublic
-  | SmallPublicKey
-  | CompressedPoint
-  | AddSubChain
-  | InvalidPublic
-  | WrongOrder
-  | UnnamedCurve
-  | UnusedParam
-  | ModifiedPrime
-  | WeakPublicKey
-  | InvalidAsn
-[@@deriving show]
-
-let invalid_asn = InvalidAsn
-
-let compressed_point = CompressedPoint
-
-let unnamed_curve = UnnamedCurve
-
-let flag_of_yojson = function
-  | `String "LowOrderPublic" ->
-      Ok LowOrderPublic
-  | `String "Twist" ->
-      Ok Twist
-  | `String "Small public key" ->
-      Ok SmallPublicKey
-  | `String "CompressedPoint" ->
-      Ok CompressedPoint
-  | `String "AddSubChain" ->
-      Ok AddSubChain
-  | `String "InvalidPublic" ->
-      Ok InvalidPublic
-  | `String "WrongOrder" ->
-      Ok WrongOrder
-  | `String "UnnamedCurve" ->
-      Ok UnnamedCurve
-  | `String "UnusedParam" ->
-      Ok UnusedParam
-  | `String "ModifiedPrime" ->
-      Ok ModifiedPrime
-  | `String "WeakPublicKey" ->
-      Ok WeakPublicKey
-  | `String "InvalidAsn" ->
-      Ok InvalidAsn
-  | `String s ->
-      Error ("Unknown flag: " ^ s)
-  | _ ->
-      Error "flag_of_yojson"
-
 type test =
   { tcId : int
   ; comment : string
@@ -93,9 +42,14 @@ type test =
   ; private_ : hex [@yojson.key "private"]
   ; shared : hex
   ; result : test_result
-  ; flags : flag list }
+  ; flags : string list }
 [@@deriving of_yojson, show]
 
+let has_ignored_flag test ~ignored_flags =
+  List.exists
+    (fun ignored_flag -> List.mem ignored_flag test.flags)
+    ignored_flags
+
 type test_group =
   { curve : json
   ; tests : test list
diff --git a/wycheproof/wycheproof.mli b/wycheproof/wycheproof.mli
index 9964538..c98b646 100644
--- a/wycheproof/wycheproof.mli
+++ b/wycheproof/wycheproof.mli
@@ -10,14 +10,6 @@ type test_result =
   | Invalid
 [@@deriving show]
 
-type flag [@@deriving show]
-
-val invalid_asn : flag
-
-val compressed_point : flag
-
-val unnamed_curve : flag
-
 type test =
   { tcId : int
   ; comment : string
@@ -26,9 +18,11 @@ type test =
   ; private_ : hex
   ; shared : hex
   ; result : test_result
-  ; flags : flag list }
+  ; flags : string list }
 [@@deriving show]
 
+val has_ignored_flag : test -> ignored_flags:string list -> bool
+
 type test_group =
   { curve : json
   ; tests : test list