diff --git a/src/lib_base/block_locator.ml b/src/lib_base/block_locator.ml
index 99b7ddea9..055a7ea9f 100644
--- a/src/lib_base/block_locator.ml
+++ b/src/lib_base/block_locator.ml
@@ -16,7 +16,26 @@ and raw = Block_header.t * Block_hash.t list
 
 let raw x = x
 
-let pp ppf loc = Block_header.pp ppf (fst loc)
+let pp ppf (hd, h_lst) =
+  let repeats = 10 in
+  let coef = 2 in
+  (* list of hashes *)
+  let rec pp_hash_list ppf (h_lst , acc , d , r) =
+    match h_lst with
+    | [] ->
+        Format.fprintf ppf ""
+    | hd :: tl ->
+        let new_d = if r > 1 then d else d * coef in
+        let new_r = if r > 1 then r - 1 else repeats in
+        Format.fprintf ppf "%a (%i)\n%a" Block_hash.pp hd acc pp_hash_list (tl , acc - d , new_d , new_r) in
+  Format.fprintf ppf "%a (head)\n%a"
+    Block_hash.pp (Block_header.hash hd)
+    pp_hash_list (h_lst , -1, 1, repeats - 1)
+
+let pp_short ppf (hd, h_lst) =
+  Format.fprintf ppf "head: %a, %d predecessors"
+    Block_hash.pp (Block_header.hash hd)
+    (List.length h_lst)
 
 let encoding =
   let open Data_encoding in
diff --git a/src/lib_base/block_locator.mli b/src/lib_base/block_locator.mli
index 4c332fc77..3a741b29b 100644
--- a/src/lib_base/block_locator.mli
+++ b/src/lib_base/block_locator.mli
@@ -17,6 +17,8 @@ val raw: t -> raw
 
 val pp : Format.formatter -> t -> unit
 
+val pp_short : Format.formatter -> t -> unit
+
 val encoding: t Data_encoding.t
 
 val compute: predecessor: (Block_hash.t -> int -> Block_hash.t option Lwt.t) ->
diff --git a/src/lib_shell_services/validation_errors.ml b/src/lib_shell_services/validation_errors.ml
index 6db5aab9e..969052149 100644
--- a/src/lib_shell_services/validation_errors.ml
+++ b/src/lib_shell_services/validation_errors.ml
@@ -136,9 +136,9 @@ let () =
     ~description:"Block locator is invalid."
     ~pp: (fun ppf (id, locator) ->
         Format.fprintf ppf
-          "Invalid block locator %a on peer %a"
-          Block_locator.pp locator
-          P2p_peer.Id.pp id)
+          "Invalid block locator on peer %a:\n%a"
+          P2p_peer.Id.pp id
+          Block_locator.pp locator)
     Data_encoding.(obj2
                      (req "id" P2p_peer.Id.encoding)
                      (req "locator" Block_locator.encoding))