diff --git a/test/validate_response.ml b/test/validate_response.ml
index 4db13e8b..b6f3a80b 100644
--- a/test/validate_response.ml
+++ b/test/validate_response.ml
@@ -87,37 +87,38 @@ let keys content =
   let* () =
     (* TODO O(n^2) *)
     v.auditors
-    |> list_iter
+    |> List.concat_map
          (fun
            AuditorKeys.
              { auditor_pub; auditor_url; auditor_name= _; denomination_keys }
          ->
            let auditor_url_hash = Hash.H64.hash auditor_url in
            denomination_keys
-           |> list_iter
+           |> List.map
                 (fun AuditorDenominationKey.{ denom_pub_h; auditor_sig } ->
-                  let open Denomination in
-                  let opt =
-                    denom_l |> List.find_opt (fun dn -> dn.h_pub = denom_pub_h)
-                  in
-                  match opt with
-                  | None -> Fmt.error "auditor denomination key not found"
-                  | Some dn ->
-                      let open Signatures.ExchangeKeyValidity in
-                      verify auditor_pub auditor_sig
-                        {
-                          auditor_url_hash;
-                          master= auditor_pub;
-                          start= dn.stamp_start;
-                          expire_withdraw= dn.stamp_expire_withdraw;
-                          expire_spend= dn.stamp_expire_deposit;
-                          expire_legal= dn.stamp_expire_legal;
-                          value= dn.value;
-                          fee_withdraw= dn.fee_withdraw;
-                          fee_deposit= dn.fee_deposit;
-                          fee_refresh= dn.fee_refresh;
-                          denom_hash= denom_pub_h;
-                        }))
+                  (denom_pub_h, auditor_url_hash, auditor_pub, auditor_sig)))
+    |> list_iter
+         (fun (denom_pub_h, auditor_url_hash, auditor_pub, auditor_sig) ->
+           let open Denomination in
+           denom_l |> List.find_opt (fun dn -> dn.h_pub = denom_pub_h)
+           |> function
+           | None -> Fmt.error "auditor denomination key not found"
+           | Some dn ->
+               let open Signatures.ExchangeKeyValidity in
+               verify auditor_pub auditor_sig
+                 {
+                   auditor_url_hash;
+                   master= auditor_pub;
+                   start= dn.stamp_start;
+                   expire_withdraw= dn.stamp_expire_withdraw;
+                   expire_spend= dn.stamp_expire_deposit;
+                   expire_legal= dn.stamp_expire_legal;
+                   value= dn.value;
+                   fee_withdraw= dn.fee_withdraw;
+                   fee_deposit= dn.fee_deposit;
+                   fee_refresh= dn.fee_refresh;
+                   denom_hash= dn.h_pub;
+                 })
   in
 
   Ok ()