diff --git a/src/pg.ml b/src/pg.ml
index 9da8a192..f11bf629 100644
--- a/src/pg.ml
+++ b/src/pg.ml
@@ -12,11 +12,14 @@ module Caqti_type = struct
 
   let amount : Amount.t t =
     let open Amount in
-    custom
-      ~encode:(fun amount -> Ok (amount.value, amount.fraction))
-      ~decode:(fun (value, fraction) ->
-        Amount.make ~sign:None ~currency:Config.currency ~value ~fraction)
-      (t2 int64 int32)
+    let intro value fraction =
+      match make ~sign:None ~currency:Config.currency ~value ~fraction with
+      | Error e -> raise (Caqti_type.Reject e)
+      | Ok v -> v
+    in
+    let p1 t = t.value in
+    let p2 t = t.fraction in
+    product intro @@ proj int64 p1 @@ proj int32 p2 @@ proj_end
 
   let age_mask : int t = Caqti_type.int