diff --git a/src/node/shell/validator.ml b/src/node/shell/validator.ml
index 8db0c0ff6..470e251e3 100644
--- a/src/node/shell/validator.ml
+++ b/src/node/shell/validator.ml
@@ -102,7 +102,10 @@ let rec may_set_head v (block: State.Valid_block.t) =
 
 (** Block validation *)
 
-type error += Invalid_operation of Operation_hash.t
+type error +=
+   | Invalid_operation of Operation_hash.t
+   | Non_increasing_timestamp
+   | Non_increasing_fitness
 
 let apply_block net db
     (pred: State.Valid_block.t) hash (block: State.Block_header.t) =
@@ -125,6 +128,18 @@ let apply_block net db
         failwith "This test network expired..."
     | None | Some _ -> return ()
   end >>=? fun () ->
+  begin
+    if Time.(pred.timestamp >= block.shell.timestamp) then
+      fail Non_increasing_timestamp
+    else
+      return ()
+  end >>=? fun () ->
+  begin
+    if Fitness.compare pred.fitness block.shell.fitness >= 0 then
+      fail Non_increasing_fitness
+    else
+      return ()
+  end >>=? fun () ->
   begin
     match pred.protocol with
     | None -> fail (State.Unknown_protocol pred.protocol_hash)
diff --git a/src/node/shell/validator.mli b/src/node/shell/validator.mli
index 5f2913ede..3148ff2ac 100644
--- a/src/node/shell/validator.mli
+++ b/src/node/shell/validator.mli
@@ -16,6 +16,10 @@ val notify_block: worker -> Block_hash.t -> State.Block_header.t -> unit Lwt.t
 
 type t
 
+type error +=
+   | Non_increasing_timestamp
+   | Non_increasing_fitness
+
 val activate: worker -> State.Net.t -> t Lwt.t
 val get: worker -> State.Net_id.t -> t tzresult Lwt.t
 val get_exn: worker -> State.Net_id.t -> t Lwt.t