diff --git a/openquake/calculators/post_risk.py b/openquake/calculators/post_risk.py
index 10af8ed0a9fe..2e834afa7a9f 100644
--- a/openquake/calculators/post_risk.py
+++ b/openquake/calculators/post_risk.py
@@ -242,7 +242,7 @@ def fix_dtypes(dic):
     fix_dtype(dic, F32, floatcolumns)
 
 
-def build_aggcurves(items, builder, num_events, aggregate_loss_curves_types):
+def build_aggcurves(items, builder, num_events, aggregate_loss_curves_types, monitor):
     """
     :param items: a list of pairs ((agg_id, rlz_id, loss_id), losses)
     :param builder: a :class:`LossCurvesMapsBuilder` instance
@@ -295,6 +295,7 @@ def store_aggcurves(oq, agg_ids, rbe_df, builder, loss_cols,
             if len(year):
                 data['year'] = year[df.event_id.to_numpy()]
             items.append([(agg_id, rlz_id, loss_id), data])
+    dstore.swmr_on()
     dic = parallel.Starmap.apply(
         build_aggcurves, (items, builder, num_events, aggtypes),
         concurrent_tasks=oq.concurrent_tasks,
diff --git a/openquake/commonlib/datastore.py b/openquake/commonlib/datastore.py
index 956edfd22261..065f09d710cf 100644
--- a/openquake/commonlib/datastore.py
+++ b/openquake/commonlib/datastore.py
@@ -134,7 +134,8 @@ def new(calc_id, oqparam, datadir=None, mode=None):
         a DataStore instance associated to the given calc_id
     """
     dstore = _read(calc_id, mode, datadir)
-    dstore['oqparam'] = oqparam
+    if 'oqparam' not in dstore:
+        dstore['oqparam'] = oqparam
     if oqparam.hazard_calculation_id:
         dstore.ppath = read(calc_id, 'r', datadir).ppath
     return dstore