diff --git a/src/proto_alpha/lib_protocol/storage.ml b/src/proto_alpha/lib_protocol/storage.ml
index 68b2e06da7600d7120a1a345f024d124d47a6ccc..1d36525c5bebc8a5abac1655ede625ea256f9ebf 100644
--- a/src/proto_alpha/lib_protocol/storage.ml
+++ b/src/proto_alpha/lib_protocol/storage.ml
@@ -312,6 +312,8 @@ module Contract = struct
     let add ctxt contract value =
       consume_serialize_gas ctxt value >>?= fun ctxt ->
       I.add ctxt contract value
+
+    let keys_unaccounted = I.keys_unaccounted
   end
 
   module Code = Make_carbonated_map_expr (struct
@@ -535,6 +537,8 @@ module Big_map = struct
       | None -> ok (ctxt, None)
       | Some value ->
           consume_deserialize_gas ctxt value >|? fun ctxt -> (ctxt, value_opt)
+
+    let keys_unaccounted = I.keys_unaccounted
   end
 end
 
diff --git a/src/proto_alpha/lib_protocol/storage_functors.ml b/src/proto_alpha/lib_protocol/storage_functors.ml
index c1d958612b36cb41b5805986b8b28cb021adeb2c..b07dcbe31d9ed40f66ca4e3306a54f8d9c3777e7 100644
--- a/src/proto_alpha/lib_protocol/storage_functors.ml
+++ b/src/proto_alpha/lib_protocol/storage_functors.ml
@@ -1073,6 +1073,18 @@ module Make_indexed_subcontext (C : Raw_context.T) (I : INDEX) :
     let add_or_remove s i v =
       match v with None -> remove s i | Some v -> add s i v
 
+    let mem_unaccounted s i = Raw_context.mem (pack s i) data_name
+
+    let fold_keys_unaccounted s ~order ~init ~f =
+      fold_keys s ~order ~init ~f:(fun i acc ->
+          mem_unaccounted s i >>= function
+          | false -> Lwt.return acc
+          | true -> f i acc)
+
+    let keys_unaccounted s =
+      fold_keys_unaccounted s ~order:`Sorted ~init:[] ~f:(fun p acc ->
+          Lwt.return (p :: acc))
+
     let () =
       let open Storage_description in
       let unpack = unpack I.args in
diff --git a/src/proto_alpha/lib_protocol/storage_sigs.ml b/src/proto_alpha/lib_protocol/storage_sigs.ml
index f1db042a94f136b114a99e1d1ca24fa00173ea1f..d6c0a2886083bc6ce72bf2782e1d894fbbd7c882 100644
--- a/src/proto_alpha/lib_protocol/storage_sigs.ml
+++ b/src/proto_alpha/lib_protocol/storage_sigs.ml
@@ -209,6 +209,10 @@ module type Non_iterable_indexed_carbonated_data_storage = sig
       Returns the freed size, and a boolean
       indicating if a value was already associated to this key. *)
   val remove : context -> key -> (Raw_context.t * int * bool) tzresult Lwt.t
+
+  (** Returns the list of all storage bucket keys.
+      Not carbonated (i.e. gas is not consumed); use with care. *)
+  val keys_unaccounted : context -> key list Lwt.t
 end
 
 module type Non_iterable_indexed_carbonated_data_storage_with_values = sig