diff --git a/openquake/baselib/parallel.py b/openquake/baselib/parallel.py
index f5313975c80b..583ed26e2176 100644
--- a/openquake/baselib/parallel.py
+++ b/openquake/baselib/parallel.py
@@ -768,6 +768,7 @@ def __init__(self, task_func, task_args=(), distribute=None,
             match = re.search(r'(\d+)', os.path.basename(h5.filename))
             self.calc_id = int(match.group(1))
         else:
+            # TODO: see if we can forbid this case
             self.calc_id = None
             h5 = hdf5.File(gettemp(suffix='.hdf5'), 'w')
             init_performance(h5)
diff --git a/openquake/baselib/workerpool.py b/openquake/baselib/workerpool.py
index 69bd10e6ee16..20dc60519e0e 100644
--- a/openquake/baselib/workerpool.py
+++ b/openquake/baselib/workerpool.py
@@ -232,10 +232,10 @@ def call(func, args, taskno, mon, executing):
 
 
 def errback(job_id, task_no, exc):
+    # NB: job_id can be None if the Starmap was invoked without h5
     from openquake.commonlib.logs import dbcmd
     dbcmd('log', job_id, datetime.utcnow(), 'ERROR',
           '%s/%s' % (job_id, task_no), str(exc))
-    raise exc
     e = exc.__class__('in job %d, task %d' % (job_id, task_no))
     raise e.with_traceback(exc.__traceback__)
 
@@ -287,9 +287,9 @@ def start(self):
                         ctrlsock.send(' '.join(executing))
                     elif isinstance(cmd, tuple):
                         func, args, taskno, mon = cmd
-                        eback = functools.partial(errback, mon.calc_id, taskno)
-                        self.pool.apply_async(call, cmd + (self.executing,),
-                                              error_callback=eback)
+                        self.pool.apply_async(
+                            call, cmd + (self.executing,),
+                            error_callback=functools.partial(errback, mon.calc_id, taskno))
                         ctrlsock.send('submitted')
                     else:
                         ctrlsock.send('unknown command')
diff --git a/openquake/calculators/event_based.py b/openquake/calculators/event_based.py
index cecd418bc845..0247e4a5672c 100644
--- a/openquake/calculators/event_based.py
+++ b/openquake/calculators/event_based.py
@@ -446,6 +446,7 @@ def build_events_from_sources(self):
             nrups = parallel.Starmap( # weighting the heavy sources
                 count_ruptures, [(src,) for src in sources
                                  if src.code in b'AMSC'],
+                h5=self.datastore.hdf5,
                 progress=logging.debug).reduce()
             # NB: multifault sources must be considered light to avoid a large
             # data transfer, even if .count_ruptures can be slow
diff --git a/openquake/commonlib/calc.py b/openquake/commonlib/calc.py
index 143057891360..b8fb99217e7e 100644
--- a/openquake/commonlib/calc.py
+++ b/openquake/commonlib/calc.py
@@ -240,7 +240,10 @@ def _save_events(self, rup_array, rgetters):
         else:
             self.datastore.swmr_on()  # before the Starmap
             acc = parallel.Starmap(
-                self.get_eid_rlz, iterargs, progress=logging.debug).reduce()
+                self.get_eid_rlz, iterargs,
+                h5=self.datastore,
+                progress=logging.debug
+            ).reduce()
         i = 0
         for ordinal, eid_rlz in sorted(acc.items()):
             for er in eid_rlz: