diff --git a/src/lib_base/block_header.ml b/src/lib_base/block_header.ml
index 257553b45..15e4adf7d 100644
--- a/src/lib_base/block_header.ml
+++ b/src/lib_base/block_header.ml
@@ -77,6 +77,11 @@ let encoding =
        shell_header_encoding
        (obj1 (req "protocol_data" Variable.bytes)))
 
+let bounded_encoding ?max_size () =
+  match max_size with
+  | None -> encoding
+  | Some max_size -> Data_encoding.check_size max_size encoding
+
 let pp ppf op =
   Data_encoding.Json.pp ppf
     (Data_encoding.Json.construct encoding op)
diff --git a/src/lib_base/block_header.mli b/src/lib_base/block_header.mli
index 1e8f54b2b..3be5b4443 100644
--- a/src/lib_base/block_header.mli
+++ b/src/lib_base/block_header.mli
@@ -28,3 +28,5 @@ type t = {
 include S.HASHABLE with type t := t
                     and type hash := Block_hash.t
 val of_bytes_exn: MBytes.t -> t
+
+val bounded_encoding: ?max_size:int -> unit -> t Data_encoding.t
diff --git a/src/lib_base/block_locator.ml b/src/lib_base/block_locator.ml
index 396922ec8..234ba685f 100644
--- a/src/lib_base/block_locator.ml
+++ b/src/lib_base/block_locator.ml
@@ -41,7 +41,17 @@ let encoding =
   (* TODO add a [description] *)
   (obj2
      (req "current_head" (dynamic_size Block_header.encoding))
-     (req "history" (dynamic_size (list Block_hash.encoding))))
+     (req "history" (Variable.list Block_hash.encoding)))
+
+let bounded_encoding ?max_header_size ?max_length () =
+  let open Data_encoding in
+  (* TODO add a [description] *)
+  (obj2
+     (req "current_head"
+        (dynamic_size
+           (Block_header.bounded_encoding ?max_size:max_header_size ())))
+     (req "history" (Variable.list ?max_length Block_hash.encoding)))
+
 
 type seed = {
   sender_id: P2p_peer.Id.t ;
diff --git a/src/lib_base/block_locator.mli b/src/lib_base/block_locator.mli
index 504d122cd..28f17bbfe 100644
--- a/src/lib_base/block_locator.mli
+++ b/src/lib_base/block_locator.mli
@@ -17,6 +17,10 @@ val raw: t -> raw
 val pp: Format.formatter -> t -> unit
 val pp_short: Format.formatter -> t -> unit
 val encoding: t Data_encoding.t
+val bounded_encoding:
+  ?max_header_size:int ->
+  ?max_length:int ->
+  unit -> t Data_encoding.t
 
 type seed = {
   sender_id: P2p_peer.Id.t ;
diff --git a/src/lib_shell/distributed_db_message.ml b/src/lib_shell/distributed_db_message.ml
index e91bfec23..28a95bb63 100644
--- a/src/lib_shell/distributed_db_message.ml
+++ b/src/lib_shell/distributed_db_message.ml
@@ -7,6 +7,28 @@
 (*                                                                        *)
 (**************************************************************************)
 
+module Bounded_encoding = struct
+
+  open Data_encoding
+
+  let block_header_max_size = ref None
+  let block_header_cache = ref Block_header.encoding
+  let block_locator_cache = ref Block_locator.encoding
+
+  let update_block_header_encoding () =
+    block_header_cache :=
+      Block_header.bounded_encoding ?max_size:!block_header_max_size () ;
+    block_locator_cache :=
+      Block_locator.bounded_encoding ?max_header_size:!block_header_max_size ()
+
+  let set_block_header_max_size max =
+    block_header_max_size := max ;
+    update_block_header_encoding ()
+  let block_header = delayed (fun () -> !block_header_cache)
+  let block_locator = delayed (fun () -> !block_locator_cache)
+
+end
+
 type t =
 
   | Get_current_branch of Chain_id.t
@@ -53,7 +75,7 @@ let encoding =
       ~title:"Current_branch"
       (obj2
          (req "chain_id" Chain_id.encoding)
-         (req "current_branch" Block_locator.encoding))
+         (req "current_branch" Bounded_encoding.block_locator))
       (function
         | Current_branch (chain_id, locator) -> Some (chain_id, locator)
         | _ -> None)
@@ -81,7 +103,7 @@ let encoding =
       ~title:"Current_head"
       (obj3
          (req "chain_id" Chain_id.encoding)
-         (req "current_block_header" (dynamic_size Block_header.encoding))
+         (req "current_block_header" (dynamic_size Bounded_encoding.block_header))
          (req "current_mempool" Mempool.encoding))
       (function
         | Current_head (chain_id, bh, mempool) -> Some (chain_id, bh, mempool)
@@ -98,7 +120,7 @@ let encoding =
 
     case ~tag:0x21
       ~title:"Block_header"
-      (obj1 (req "block_header" Block_header.encoding))
+      (obj1 (req "block_header" Bounded_encoding.block_header))
       (function
         | Block_header bh -> Some bh
         | _ -> None)
diff --git a/src/lib_shell/distributed_db_message.mli b/src/lib_shell/distributed_db_message.mli
index 29d43cdbe..d44213dea 100644
--- a/src/lib_shell/distributed_db_message.mli
+++ b/src/lib_shell/distributed_db_message.mli
@@ -40,3 +40,7 @@ type t =
 val cfg : t P2p.message_config
 
 val pp_json : Format.formatter -> t -> unit
+
+module Bounded_encoding : sig
+  val set_block_header_max_size: int option -> unit
+end