diff --git a/src/bin_signature.ml b/src/bin_signature.ml
index 84fdbac4..5fe0ad58 100644
--- a/src/bin_signature.ml
+++ b/src/bin_signature.ml
@@ -88,7 +88,7 @@ module DenominationKeyAnnouncementPS = struct
   (* TODO taler_signatures purpose
      we use TALER_SIGNATURE_SM_RSA_DENOMINATION_KEY instead here *)
   (* purpose.purpose = TALER_SIGNATURE_SM_DENOMINATION_KEY *)
-  type t = {
+  type r = {
     h_denom_pub: DenominationHash.t;
     h_section_name: Hash_64_cstr.t;
     anchor_time: TimeAbsoluteNBO.t;
@@ -107,6 +107,18 @@ module DenominationKeyAnnouncementPS = struct
     |+ field TimeAbsoluteNBO.bin (fun t -> t.anchor_time)
     |+ field TimeRelativeNBO.bin (fun t -> t.duration_withdraw)
     |> sealr
+
+  module type SIG = sig
+    type t
+
+    val f : (string -> Crypto.EddsaSignature.t) -> r -> t
+  end
+
+  module Sig : SIG = struct
+    type t = Crypto.EddsaSignature.t
+
+    let f signf r = signf @@ Bin.to_string bin r
+  end
 end
 
 module SigningKeyAnnouncementPS = struct
diff --git a/src/management.ml b/src/management.ml
index c338635d..1b9120a9 100644
--- a/src/management.ml
+++ b/src/management.ml
@@ -31,8 +31,9 @@ let mk_future_denom denom_key_signf
     let duration_withdraw =
       Timestamp.diff stamp_start stamp_expire_withdraw |> Timestamp.of_span_exn
     in
-    let ps = { h_denom_pub; h_section_name; anchor_time; duration_withdraw } in
-    ps |> Bin.to_string bin |> denom_key_signf
+    { h_denom_pub; h_section_name; anchor_time; duration_withdraw }
+    |> Bin.to_string bin
+    |> denom_key_signf
   in
   FutureDenom.
     {
@@ -60,8 +61,9 @@ let mk_future_signkey signkey_signf
     let duration =
       Timestamp.diff stamp_start stamp_expire |> Timestamp.of_span_exn
     in
-    let ps = { exchange_pub; anchor_time; duration } in
-    ps |> Bin.to_string bin |> signkey_signf
+    { exchange_pub; anchor_time; duration }
+    |> Bin.to_string bin
+    |> signkey_signf
   in
   FutureSignKey.
     { key= pub; stamp_start; stamp_expire; stamp_end; signkey_secmod_sig }