diff --git a/src/proto/alpha/roll_storage.ml b/src/proto/alpha/roll_storage.ml
index 171aa5840..5a3c3439d 100644
--- a/src/proto/alpha/roll_storage.ml
+++ b/src/proto/alpha/roll_storage.ml
@@ -188,12 +188,15 @@ module Contract = struct
     Storage.Roll.Contract_change.get c contract >>=? fun change ->
     loop c change >>=? fun (c, change) ->
     Lwt.return Tez_repr.(change -? amount) >>=? fun change ->
-    Storage.Roll.Contract_change.set c contract change
+    if Tez_repr.(change = zero) then
+      Storage.Roll.Contract_change.delete c contract
+    else
+      Storage.Roll.Contract_change.set c contract change
 
   let assert_empty c contract =
-    Storage.Roll.Contract_change.get c contract >>=? fun change ->
+    Storage.Roll.Contract_change.mem c contract >>= fun change ->
     Storage.Roll.Contract_roll_list.get c contract >>=? fun roll_list ->
-    fail_unless (Tez_repr.(change = zero) &&
+    fail_unless (not change &&
                  match roll_list with None -> true | Some _ -> false)
       Deleted_contract_owning_rolls