diff --git a/src/api.ml b/src/api.ml
index 045aa4b4..19b615cb 100644
--- a/src/api.ml
+++ b/src/api.ml
@@ -924,3 +924,42 @@ module RecoupDenoms = struct
     |> mem "h_denom_pub" HashCode.jsont ~enc:h_denom_pub
     |> finish
 end
+
+module DenomCommon = struct
+  type t = {
+    master_sig: DenominationKeyValidityPS.t;
+    stamp_start: Timestamp.t;
+    stamp_expire_withdraw: Timestamp.t;
+    stamp_expire_deposit: Timestamp.t;
+    stamp_expire_legal: Timestamp.t;
+    lost: bool option;
+  }
+
+  let jsont =
+    let make master_sig stamp_start stamp_expire_withdraw stamp_expire_deposit
+        stamp_expire_legal lost =
+      {
+        master_sig;
+        stamp_start;
+        stamp_expire_withdraw;
+        stamp_expire_deposit;
+        stamp_expire_legal;
+        lost;
+      }
+    in
+    let master_sig v = v.master_sig in
+    let stamp_start v = v.stamp_start in
+    let stamp_expire_withdraw v = v.stamp_expire_withdraw in
+    let stamp_expire_deposit v = v.stamp_expire_deposit in
+    let stamp_expire_legal v = v.stamp_expire_legal in
+    let lost v = v.lost in
+    let open Jsont.Object in
+    map ~kind:"DenomCommon" make
+    |> mem "master_sig" DenominationKeyValidityPS.jsont ~enc:master_sig
+    |> mem "stamp_start" Timestamp.jsont ~enc:stamp_start
+    |> mem "stamp_expire_withdraw" Timestamp.jsont ~enc:stamp_expire_withdraw
+    |> mem "stamp_expire_deposit" Timestamp.jsont ~enc:stamp_expire_deposit
+    |> mem "stamp_expire_legal" Timestamp.jsont ~enc:stamp_expire_legal
+    |> mem "lost" (Jsont.option Jsont.bool) ~enc:lost
+    |> finish
+end