diff --git a/src/proto_alpha/lib_protocol/sc_rollup_storage.ml b/src/proto_alpha/lib_protocol/sc_rollup_storage.ml
index f9132b4302510130b69df374a5d120dcc8d2c1fb..7a7c34e7180e6d3908ebdc86b459ed22f503cade 100644
--- a/src/proto_alpha/lib_protocol/sc_rollup_storage.ml
+++ b/src/proto_alpha/lib_protocol/sc_rollup_storage.ml
@@ -39,7 +39,7 @@ let originate ctxt ~kind ~boot_sector ~parameters_ty =
   Store.Parameters_type.add ctxt address parameters_ty
   >>=? fun (ctxt, param_ty_size_diff, _added) ->
   let inbox = Sc_rollup_inbox_repr.empty address level.level in
-  Store.Inbox.init ctxt address inbox >>=? fun (ctxt, size_diff) ->
+  Store.Inbox.init ctxt address inbox >>=? fun (ctxt, inbox_size_diff) ->
   Store.Last_cemented_commitment.init ctxt address Commitment_hash.zero
   >>=? fun (ctxt, lcc_size_diff) ->
   Store.Staker_count.init ctxt address 0l >>=? fun (ctxt, stakers_size_diff) ->
@@ -52,7 +52,8 @@ let originate ctxt ~kind ~boot_sector ~parameters_ty =
   let size =
     Z.of_int
       (origination_size + stored_kind_size + boot_sector_size + addresses_size
-     + size_diff + lcc_size_diff + stakers_size_diff + param_ty_size_diff)
+     + inbox_size_diff + lcc_size_diff + stakers_size_diff + param_ty_size_diff
+      )
   in
   return (address, size, ctxt)