diff --git a/src/proto_alpha/lib_protocol/src/seed_storage.ml b/src/proto_alpha/lib_protocol/src/seed_storage.ml
index 0819b32bd..5dfb379b0 100644
--- a/src/proto_alpha/lib_protocol/src/seed_storage.ml
+++ b/src/proto_alpha/lib_protocol/src/seed_storage.ml
@@ -56,7 +56,8 @@ let compute_for_cycle c ~revealed cycle =
             Storage.Seed.Nonce.delete c level >>=? fun c ->
             return (c, random_seed, u :: unrevealed)
       in
-      Storage.Seed.For_cycle.get c previous_cycle >>=? fun seed ->
+      Storage.Seed.For_cycle.get c previous_cycle >>=? fun prev_seed ->
+      let seed = Seed_repr.deterministic_seed prev_seed in
       fold_left_s combine (c, seed, []) levels >>=? fun (c, seed, unrevealed) ->
       Storage.Seed.For_cycle.init c cycle seed >>=? fun c ->
       return (c, unrevealed)
@@ -102,6 +103,6 @@ let cycle_end ctxt last_cycle =
   end >>=? fun ctxt ->
   match Cycle_repr.pred last_cycle with
   | None -> return (ctxt, [])
-  | Some revealed ->
+  | Some revealed -> (* cycle with revelations *)
       let inited_seed_cycle = Cycle_repr.add last_cycle (preserved+1) in
       compute_for_cycle ctxt ~revealed inited_seed_cycle
diff --git a/src/proto_alpha/lib_protocol/src/seed_storage.mli b/src/proto_alpha/lib_protocol/src/seed_storage.mli
index 76f52df66..8219c59bc 100644
--- a/src/proto_alpha/lib_protocol/src/seed_storage.mli
+++ b/src/proto_alpha/lib_protocol/src/seed_storage.mli
@@ -12,6 +12,8 @@ type error +=
                  cycle : Cycle_repr.t ;
                  latest : Cycle_repr.t } (* `Permanent *)
 
+(** Generates the first [preserved_cycles+2] seeds for which
+    there are no nonces. *)
 val init:
   Raw_context.t -> Raw_context.t tzresult Lwt.t