diff --git a/lib_embedded_client_genesis/client_proto_main.ml b/lib_embedded_client_genesis/client_proto_main.ml
index 5eeb7270a..1b891e943 100644
--- a/lib_embedded_client_genesis/client_proto_main.ml
+++ b/lib_embedded_client_genesis/client_proto_main.ml
@@ -23,24 +23,14 @@ let call_error_service1 rpc_config s block a1 =
   | Ok (Ok v) -> return v
   | Error _ as err -> Lwt.return err
 
-let forge_block
-    rpc_config block net_id ?(timestamp = Time.now ()) command fitness =
+let bake rpc_config ?(timestamp = Time.now ()) block command seckey =
   let block = Client_rpcs.last_baked_block block in
-  Client_node_rpcs.Blocks.info rpc_config block >>=? fun pred ->
-  let proto_level =
-    match command with
-    | Data.Command.Activate _ -> 1
-    | Data.Command.Activate_testnet _ -> 0 in
-  call_service1 rpc_config
-    Services.Forge.block block
-    ((net_id, Int32.succ pred.level, proto_level,
-      pred.hash, timestamp, fitness), command)
-
-let bake rpc_config ?timestamp block command fitness seckey =
-  let block = Client_rpcs.last_baked_block block in
-  Client_node_rpcs.Blocks.info rpc_config block >>=? fun bi ->
-  forge_block
-    rpc_config ?timestamp block bi.net_id command fitness >>=? fun blk ->
+  let proto_header = Data_encoding.Binary.to_bytes Data.Command.encoding command in
+  Client_node_rpcs.Blocks.preapply
+    rpc_config block ~timestamp ~proto_header [] >>=? fun { shell_header } ->
+  let blk =
+    Data_encoding.Binary.to_bytes Block_header.encoding
+      { shell = shell_header ; proto = proto_header } in
   let signed_blk = Ed25519.Signature.append seckey blk in
   Client_node_rpcs.inject_block rpc_config signed_blk []
 
@@ -87,7 +77,8 @@ let commands () =
         let fitness =
           Tezos_embedded_raw_protocol_alpha.Fitness_repr.from_int64 fitness in
         bake cctxt ?timestamp cctxt#block
-          (Activate { protocol = hash ; validation_passes }) fitness seckey >>=? fun hash ->
+          (Activate { protocol = hash ; validation_passes ; fitness })
+          seckey >>=? fun hash ->
         cctxt#answer "Injected %a" Block_hash.pp_short hash >>= fun () ->
         return ()
       end ;
@@ -96,11 +87,7 @@ let commands () =
       args
       (prefixes [ "fork" ; "test" ; "protocol" ]
        @@ Protocol_hash.param ~name:"version" ~desc:"Protocol version (b58check)"
-       @@ prefixes [ "with" ; "fitness" ]
-       @@ param ~name:"fitness"
-         ~desc:"Hardcoded fitness of the first block (integer)"
-         int64_parameter
-       @@ prefixes [ "and" ; "passes" ]
+       @@ prefixes [ "with" ; "passes" ]
        @@ param ~name:"passes"
          ~desc:"Hardcoded number of validation passes (integer)"
          int_parameter
@@ -108,14 +95,12 @@ let commands () =
        @@ Ed25519.Secret_key.param
          ~name:"password" ~desc:"Dictator's key"
        @@ stop)
-      begin fun timestamp hash fitness validation_passes seckey cctxt ->
-        let fitness =
-          Tezos_embedded_raw_protocol_alpha.Fitness_repr.from_int64 fitness in
+      begin fun timestamp hash validation_passes seckey cctxt ->
         bake cctxt ?timestamp cctxt#block
           (Activate_testnet { protocol = hash ;
                               validation_passes ;
                               delay = Int64.mul 24L 3600L })
-          fitness seckey >>=? fun hash ->
+          seckey >>=? fun hash ->
         cctxt#answer "Injected %a" Block_hash.pp_short hash >>= fun () ->
         return ()
       end ;
diff --git a/lib_embedded_client_genesis/client_proto_main.mli b/lib_embedded_client_genesis/client_proto_main.mli
index 1c39d356d..9a13c3a7b 100644
--- a/lib_embedded_client_genesis/client_proto_main.mli
+++ b/lib_embedded_client_genesis/client_proto_main.mli
@@ -14,7 +14,6 @@ val bake:
   ?timestamp: Time.t ->
   Client_node_rpcs.Blocks.block ->
   Data.Command.t ->
-  Fitness.t ->
   Environment.Ed25519.Secret_key.t ->
   Block_hash.t tzresult Lwt.t
 
diff --git a/lib_embedded_protocol_genesis/src/data.ml b/lib_embedded_protocol_genesis/src/data.ml
index b843c468a..fb91ad9d7 100644
--- a/lib_embedded_protocol_genesis/src/data.ml
+++ b/lib_embedded_protocol_genesis/src/data.ml
@@ -14,6 +14,7 @@ module Command = struct
     | Activate of {
         protocol: Protocol_hash.t ;
         validation_passes: int ;
+        fitness: Fitness.t ;
       }
 
     (* Activate a protocol as a testnet *)
@@ -37,16 +38,17 @@ module Command = struct
     union ~tag_size:`Uint8 [
       case (Tag 0)
         (mk_case "activate"
-           (obj2
+           (obj3
               (req "hash" Protocol_hash.encoding)
               (req "validation_passes" uint8)
+              (req "fitness" Fitness.encoding)
            ))
         (function
-          | Activate { protocol ; validation_passes } ->
-              Some (protocol, validation_passes)
+          | Activate { protocol ; validation_passes ; fitness} ->
+              Some (protocol, validation_passes, fitness)
           | _ -> None)
-        (fun (protocol, validation_passes) ->
-           Activate { protocol ; validation_passes }) ;
+        (fun (protocol, validation_passes, fitness) ->
+           Activate { protocol ; validation_passes ; fitness }) ;
       case (Tag 1)
         (mk_case "activate_testnet"
            (obj3
diff --git a/lib_embedded_protocol_genesis/src/main.ml b/lib_embedded_protocol_genesis/src/main.ml
index 4f3c91ff1..8c69789e1 100644
--- a/lib_embedded_protocol_genesis/src/main.ml
+++ b/lib_embedded_protocol_genesis/src/main.ml
@@ -81,17 +81,9 @@ let precheck_block
   Lwt.return (parse_block raw_block) >>=? fun _ ->
   return ()
 
-let begin_application
-    ~predecessor_context:ctxt
-    ~predecessor_timestamp:_
-    ~predecessor_fitness:_
-    raw_block =
-  Data.Init.may_initialize ctxt >>=? fun ctxt ->
-  Lwt.return (parse_block raw_block) >>=? fun block ->
-  check_signature ctxt block >>=? fun () ->
-  let fitness = raw_block.shell.fitness in
-  match block.command with
-  | Data.Command.Activate { protocol = hash ; validation_passes } ->
+let prepare_application ctxt command timestamp fitness =
+  match command with
+  | Data.Command.Activate { protocol = hash ; validation_passes ; fitness } ->
       let message =
         Some (Format.asprintf "activate %a" Protocol_hash.pp_short hash) in
       Updater.activate ctxt hash >>= fun ctxt ->
@@ -103,7 +95,7 @@ let begin_application
   | Activate_testnet { protocol = hash ; validation_passes ; delay } ->
       let message =
         Some (Format.asprintf "activate testnet %a" Protocol_hash.pp_short hash) in
-      let expiration = Time.add raw_block.shell.timestamp delay in
+      let expiration = Time.add timestamp delay in
       Updater.fork_test_network ctxt ~protocol:hash ~expiration >>= fun ctxt ->
       return { Updater.message ; context = ctxt ; fitness ;
                max_operations_ttl = 0 ;
@@ -111,21 +103,40 @@ let begin_application
                  Array.to_list (Array.make validation_passes 0) ;
                max_operation_data_length = 0 }
 
+
+let begin_application
+    ~predecessor_context:ctxt
+    ~predecessor_timestamp:_
+    ~predecessor_fitness:_
+    raw_block =
+  Data.Init.may_initialize ctxt >>=? fun ctxt ->
+  Lwt.return (parse_block raw_block) >>=? fun block ->
+  check_signature ctxt block >>=? fun () ->
+  prepare_application ctxt block.command block.shell.timestamp block.shell.fitness
+
 let begin_construction
-    ~predecessor_context:context
+    ~predecessor_context:ctxt
     ~predecessor_timestamp:_
     ~predecessor_level:_
     ~predecessor_fitness:fitness
     ~predecessor:_
-    ~timestamp:_
-    ?proto_header:_
+    ~timestamp
+    ?proto_header
     () =
-  (* Dummy result. *)
-  return { Updater.message = None ; context ;
-           fitness ; max_operations_ttl = 0 ;
-           max_operation_data_length = 0 ;
-           max_number_of_operations = [] ;
-         }
+  match proto_header with
+  | None ->
+      (* Dummy result. *)
+      return { Updater.message = None ; context = ctxt ;
+               fitness ; max_operations_ttl = 0 ;
+               max_operation_data_length = 0 ;
+               max_number_of_operations = [] ;
+             }
+  | Some command ->
+      match Data_encoding.Binary.of_bytes Data.Command.encoding command with
+      | None -> failwith "Failed to parse proto header"
+      | Some command ->
+          Data.Init.may_initialize ctxt >>=? fun ctxt ->
+          prepare_application ctxt command timestamp fitness
 
 let apply_operation _vctxt _ =
   Lwt.return (Error []) (* absurd *)
diff --git a/lib_embedded_protocol_genesis/src/services.ml b/lib_embedded_protocol_genesis/src/services.ml
index b1716249f..2709c775c 100644
--- a/lib_embedded_protocol_genesis/src/services.ml
+++ b/lib_embedded_protocol_genesis/src/services.ml
@@ -69,7 +69,8 @@ let rpc_services : Updater.rpc_context RPC_directory.t =
       (fun _ctxt () ((_net_id, level, proto_level, predecessor,
                       timestamp, fitness), command) ->
         let shell = { Block_header.level ; proto_level ; predecessor ;
-                      timestamp ; fitness ; validation_passes = 0 ; operations_hash } in
+                      timestamp ; fitness ; validation_passes = 0 ;
+                      operations_hash } in
         let bytes = Data.Command.forge shell command in
         RPC_answer.return bytes) in
   dir
diff --git a/test/proto_alpha/proto_alpha_helpers.ml b/test/proto_alpha/proto_alpha_helpers.ml
index 5665260c7..371f88227 100644
--- a/test/proto_alpha/proto_alpha_helpers.ml
+++ b/test/proto_alpha/proto_alpha_helpers.ml
@@ -42,8 +42,9 @@ let activate_alpha () =
   let fitness = Fitness_repr.from_int64 0L in
   Tezos_embedded_client_genesis.Client_proto_main.bake
     (new Client_rpcs.http_ctxt !rpc_config) (`Head 0)
-    (Activate  { protocol = Client_proto_main.protocol ; validation_passes = 1})
-    fitness dictator_sk
+    (Activate  { protocol = Client_proto_main.protocol ; validation_passes = 1 ;
+                 fitness })
+    dictator_sk
 
 let init ?(sandbox = "sandbox.json") ?rpc_port () =
   begin