diff --git a/src/lib_shell/mempool_worker.ml b/src/lib_shell/mempool_worker.ml
index 8711a8844..48f756080 100644
--- a/src/lib_shell/mempool_worker.ml
+++ b/src/lib_shell/mempool_worker.ml
@@ -51,7 +51,7 @@ module type T = sig
   val shutdown : t -> unit Lwt.t
 
   (** parse a new operation and add it to the mempool context *)
-  val parse : t -> Operation.t -> operation tzresult
+  val parse : Operation.t -> operation tzresult
 
   (** validate a new operation and add it to the mempool context *)
   val validate : t -> operation -> result tzresult Lwt.t
@@ -218,56 +218,61 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
             (Format.pp_print_list Error_monad.pp) errors
   end
 
-  (* operations' cache. used for memoization *)
-  module Cache = struct
+  (* parsed operations' cache. used for memoization *)
+  module ParsedCache = struct
 
-    type t = {
-      operations : result Operation_hash.Table.t ;
-      parsed_operations : operation tzresult Operation_hash.Table.t ;
-    }
+    type t = operation tzresult Operation_hash.Table.t
 
     let encoding =
-      let open Data_encoding in
-      conv
-        (fun { operations ; parsed_operations } -> (operations, parsed_operations))
-        (fun (operations, parsed_operations) -> { operations ; parsed_operations })
-        (obj2
-           (req "operations" (Operation_hash.Table.encoding result_encoding))
-           (req "parsed_operations"
-              (Operation_hash.Table.encoding
-                 (Error_monad.result_encoding operation_encoding)))
-        )
+      (Operation_hash.Table.encoding
+         (Error_monad.result_encoding operation_encoding))
 
-    let create () =
-      { operations = Operation_hash.Table.create 1000 ;
-        parsed_operations = Operation_hash.Table.create 1000
-      }
+    let create () : t =
+      Operation_hash.Table.create 1000
 
-    let add_validated t parsed_op result =
-      Operation_hash.Table.replace t.operations parsed_op.hash result
-
-    let add_parsed t raw_op parsed_op =
+    let add t raw_op parsed_op =
       let hash = Operation.hash raw_op in
-      Operation_hash.Table.replace t.parsed_operations hash parsed_op
+      Operation_hash.Table.replace t hash parsed_op
 
-    let mem_validated t parsed_op =
-      Operation_hash.Table.mem t.operations parsed_op.hash
-
-    let mem_parsed t raw_op =
+    let mem t raw_op =
       let hash = Operation.hash raw_op in
-      Operation_hash.Table.mem t.parsed_operations hash
+      Operation_hash.Table.mem t hash
 
-    let find_validated_opt t parsed_op =
-      Operation_hash.Table.find_opt t.operations parsed_op.hash
-
-    let find_parsed_opt t raw_op =
+    let find_opt t raw_op =
       let hash = Operation.hash raw_op in
-      Operation_hash.Table.find_opt t.parsed_operations hash
+      Operation_hash.Table.find_opt t hash
 
-    let iter_validated f t =
-      Operation_hash.Table.iter f t.operations
+    let find_hash_opt t hash =
+      Operation_hash.Table.find_opt t hash
 
-    let to_mempool t =
+    let rem t hash =
+      Operation_hash.Table.remove t hash
+
+  end
+
+  (* validated operations' cache. used for memoization *)
+  module ValidatedCache = struct
+
+    type t = result Operation_hash.Table.t
+
+    let encoding =
+      Operation_hash.Table.encoding result_encoding
+
+    let create () = Operation_hash.Table.create 1000
+
+    let add t parsed_op result =
+      Operation_hash.Table.replace t parsed_op.hash result
+
+    let mem t parsed_op =
+      Operation_hash.Table.mem t parsed_op.hash
+
+    let find_opt t parsed_op =
+      Operation_hash.Table.find_opt t parsed_op.hash
+
+    let iter f t =
+      Operation_hash.Table.iter f t
+
+    let to_mempool t parsed_cache =
       let empty = {
         Proto_services.Mempool.applied = [] ;
         refused = Operation_hash.Map.empty ;
@@ -283,7 +288,7 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
         { Proto.shell = op.shell ; protocol_data } in
       Operation_hash.Table.fold
         (fun hash result acc ->
-           match Operation_hash.Table.find_opt t.parsed_operations hash with
+           match ParsedCache.find_hash_opt parsed_cache hash with
            (* XXX this invariant should be better enforced *)
            | None | Some (Error _) -> assert false
            | Some (Ok op) -> begin
@@ -319,11 +324,9 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
                  }
                | _ -> acc
              end)
-        t.operations empty
+        t empty
 
-    let clear t =
-      Operation_hash.Table.clear t.operations;
-      Operation_hash.Table.clear t.parsed_operations
+    let clear t = Operation_hash.Table.clear t
 
   end
 
@@ -341,7 +344,7 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
         (* state of the validator. this is updated at each apply_operation *)
         mutable validation_state : Proto.validation_state ;
 
-        cache : Cache.t ;
+        cache : ValidatedCache.t ;
 
         (* live blocks and operations, initialized at worker launch *)
         live_blocks : Block_hash.Set.t ;
@@ -356,7 +359,7 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
         parameters : parameters ;
       }
 
-    type view = { cache : Cache.t }
+    type view = { cache : ValidatedCache.t }
 
     let view (state : state) _ : view = { cache = state.cache }
 
@@ -365,7 +368,7 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
       conv
         (fun { cache } -> cache)
         (fun cache -> { cache })
-        Cache.encoding
+        ValidatedCache.encoding
 
     let pp ppf _view =
       Format.fprintf ppf "lots of operations"
@@ -378,6 +381,8 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
 
   type t = Worker.infinite Worker.queue Worker.t
 
+  let parsed_cache = ParsedCache.create ()
+
   let debug w =
     Format.kasprintf (fun msg -> Worker.record_event w (Debug msg))
 
@@ -443,7 +448,7 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
 
   (*** end prevalidation ***)
 
-  let parse_helper (_ : t) raw_op =
+  let parse_helper raw_op =
     let hash = Operation.hash raw_op in
     let size = Data_encoding.Binary.length Operation.encoding raw_op in
     if size > Proto.max_operation_data_length then
@@ -480,10 +485,10 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
   (* memoization is done only at on_* level *)
   let on_validate w parsed_op =
     let state = Worker.state w in
-    match Cache.find_validated_opt state.cache parsed_op with
+    match ValidatedCache.find_opt state.cache parsed_op with
     | None | Some (Branch_delayed _) ->
         validate_helper w parsed_op >>= fun result ->
-        Cache.add_validated state.cache parsed_op result;
+        ValidatedCache.add state.cache parsed_op result;
         (* operations are notified only the first time *)
         notify_helper w result parsed_op.raw ;
         Lwt.return result
@@ -500,9 +505,13 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
     Chain.data chain_state >>= fun {
       current_mempool = _mempool ;
       live_blocks ; live_operations } ->
+    (* remove all operations that are already included *)
+    Operation_hash.Set.iter (fun hash ->
+        ParsedCache.rem parsed_cache hash
+      ) live_operations;
     Lwt.return {
       validation_state ;
-      cache = Cache.create () ;
+      cache = ValidatedCache.create () ;
       live_blocks ;
       live_operations ;
       operation_stream = Lwt_watcher.create_input ();
@@ -512,11 +521,11 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
   let on_close w =
     let state = Worker.state w in
     Lwt_watcher.shutdown_input state.operation_stream;
-    Cache.iter_validated (fun hash _ ->
+    ValidatedCache.iter (fun hash _ ->
         Distributed_db.Operation.clear_or_cancel
           state.parameters.chain_db hash)
       state.cache ;
-    Cache.clear state.cache;
+    ValidatedCache.clear state.cache;
     Lwt.return_unit
 
   let on_error w r st errs =
@@ -557,12 +566,11 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
     Worker.push_request_and_wait t (Request.Validate parsed_op)
 
   (* atomic parse + memoization *)
-  let parse t raw_op =
-    let state = Worker.state t in
-    begin match Cache.find_parsed_opt state.cache raw_op with
+  let parse raw_op =
+    begin match ParsedCache.find_opt parsed_cache raw_op with
       | None ->
-          let parsed_op = parse_helper t raw_op in
-          Cache.add_parsed state.cache raw_op parsed_op;
+          let parsed_op = parse_helper raw_op in
+          ParsedCache.add parsed_cache raw_op parsed_op;
           parsed_op
       | Some parsed_op -> parsed_op
     end
@@ -577,7 +585,7 @@ module Make(Proto: Registered_protocol.T) : T with module Proto = Proto = struct
       (Proto_services.S.Mempool.pending_operations RPC_path.open_root)
       (fun w () () ->
          let state = Worker.state w in
-         RPC_answer.return (Cache.to_mempool state.cache)
+         RPC_answer.return (ValidatedCache.to_mempool state.cache parsed_cache)
       )
 
   let monitor_rpc_directory : t RPC_directory.t =
diff --git a/src/lib_shell/mempool_worker.mli b/src/lib_shell/mempool_worker.mli
index e3def9ea2..be9fdd4a4 100644
--- a/src/lib_shell/mempool_worker.mli
+++ b/src/lib_shell/mempool_worker.mli
@@ -51,8 +51,8 @@ module type T = sig
   val create : limits -> Distributed_db.chain_db -> t tzresult Lwt.t
   val shutdown : t -> unit Lwt.t
 
-  (** parse a new operation and add it to the mempool context *)
-  val parse : t -> Operation.t -> operation tzresult
+  (** parse a new operation *)
+  val parse : Operation.t -> operation tzresult
 
   (** validate a new operation and add it to the mempool context *)
   val validate : t -> operation -> result tzresult Lwt.t