diff --git a/src/node/shell/distributed_db.ml b/src/node/shell/distributed_db.ml
index fb45a0010..1cd1fda88 100644
--- a/src/node/shell/distributed_db.ml
+++ b/src/node/shell/distributed_db.ml
@@ -20,7 +20,12 @@ type 'a request_param = {
 }
 
 module Make_raw
-    (Hash : sig type t end)
+    (Hash : sig
+       type t
+       val name : string
+       val encoding : t Data_encoding.t
+       val pp : Format.formatter -> t -> unit
+      end)
     (Disk_table :
        Distributed_db_functors.DISK_TABLE with type key := Hash.t)
     (Memory_table :
@@ -155,7 +160,14 @@ module Raw_operation_hashes = struct
 
   include
     Make_raw
-      (struct type t = Block_hash.t * int end)
+      (struct
+        type t = Block_hash.t * int
+        let name = "raw_operation_hash"
+        let pp ppf (h, n) = Format.fprintf ppf "%a:%d" Block_hash.pp h n
+        let encoding =
+          let open Data_encoding in
+          obj2 (req "block" Block_hash.encoding) (req "index" uint16)
+      end)
       (Operation_hashes_storage)
       (Operations_table)
       (struct
@@ -217,7 +229,14 @@ end
 module Raw_operations = struct
   include
     Make_raw
-      (struct type t = Block_hash.t * int end)
+      (struct
+        type t = Block_hash.t * int
+        let name = "raw_operation"
+        let pp ppf (h, n) = Format.fprintf ppf "%a:%d" Block_hash.pp h n
+        let encoding =
+          let open Data_encoding in
+          obj2 (req "block" Block_hash.encoding) (req "index" uint16)
+      end)
       (Operations_storage)
       (Operations_table)
       (struct
diff --git a/src/node/shell/distributed_db_functors.ml b/src/node/shell/distributed_db_functors.ml
index 7a3e08c93..26c9bcaa9 100644
--- a/src/node/shell/distributed_db_functors.ml
+++ b/src/node/shell/distributed_db_functors.ml
@@ -70,7 +70,12 @@ module type PRECHECK = sig
 end
 
 module Make_table
-    (Hash : sig type t end)
+    (Hash : sig
+       type t
+       val name : string
+       val encoding : t Data_encoding.t
+       val pp : Format.formatter -> t -> unit
+     end)
     (Disk_table : DISK_TABLE with type key := Hash.t)
     (Memory_table : MEMORY_TABLE with type key := Hash.t)
     (Scheduler : SCHEDULER_EVENTS with type key := Hash.t)
@@ -123,6 +128,17 @@ end = struct
 
   type error += Missing_data of key
 
+  let () =
+    Error_monad.register_error_kind `Permanent
+      ~id: ("distributed_db." ^ Hash.name ^ ".missing")
+      ~title: ("Missing " ^ Hash.name)
+      ~description: ("Some " ^ Hash.name ^ " is missing from the distributed db")
+      ~pp: (fun ppf key ->
+          Format.fprintf ppf "Missing %s %a" Hash.name Hash.pp key)
+      (Data_encoding.obj1 (Data_encoding.req "key" Hash.encoding))
+      (function Missing_data key -> Some key | _ -> None)
+      (fun key -> Missing_data key)
+
   let read s k =
     match Memory_table.find s.memory k with
     | exception Not_found ->
diff --git a/src/node/shell/distributed_db_functors.mli b/src/node/shell/distributed_db_functors.mli
index dba1d6bf2..083f4ce20 100644
--- a/src/node/shell/distributed_db_functors.mli
+++ b/src/node/shell/distributed_db_functors.mli
@@ -71,7 +71,12 @@ module type PRECHECK = sig
 end
 
 module Make_table
-    (Hash : sig type t end)
+    (Hash : sig
+       type t
+       val name : string
+       val encoding : t Data_encoding.t
+       val pp : Format.formatter -> t -> unit
+     end)
     (Disk_table : DISK_TABLE with type key := Hash.t)
     (Memory_table : MEMORY_TABLE with type key := Hash.t)
     (Scheduler : SCHEDULER_EVENTS with type key := Hash.t)