diff --git a/chrono/api/views.py b/chrono/api/views.py
index 10806962..cc8fadc8 100644
--- a/chrono/api/views.py
+++ b/chrono/api/views.py
@@ -1320,7 +1320,7 @@ class Fillslots(APIView):
     def post(self, request, agenda_identifier=None, event_identifier=None, format=None):
         return self.fillslot(request=request, agenda_identifier=agenda_identifier, format=format)
 
-    def fillslot(self, request, agenda_identifier=None, slots=None, format=None):
+    def fillslot(self, request, agenda_identifier=None, slots=None, format=None, retry=False):
         slots = slots or []
         multiple_booking = bool(not slots)
         try:
@@ -1550,25 +1550,41 @@ class Fillslots(APIView):
                         if (event.booked_places + places_count) > event.places:
                             raise APIError(N_('sold out'))
 
-        with transaction.atomic():
-            if to_cancel_booking:
-                cancelled_booking_id = to_cancel_booking.pk
-                to_cancel_booking.cancel()
+        try:
+            with transaction.atomic():
+                if to_cancel_booking:
+                    cancelled_booking_id = to_cancel_booking.pk
+                    to_cancel_booking.cancel()
 
-            # now we have a list of events, book them.
-            primary_booking = None
-            for event in events:
-                if agenda.accept_meetings():
-                    event.save()
-                    if resources:
-                        event.resources.add(*resources)
-                for dummy in range(places_count):
-                    new_booking = make_booking(
-                        event, payload, extra_data, primary_booking, in_waiting_list, color
-                    )
-                    new_booking.save()
-                    if primary_booking is None:
-                        primary_booking = new_booking
+                # now we have a list of events, book them.
+                primary_booking = None
+                for event in events:
+                    if agenda.accept_meetings():
+                        event.save()
+                        if resources:
+                            event.resources.add(*resources)
+                    for dummy in range(places_count):
+                        new_booking = make_booking(
+                            event, payload, extra_data, primary_booking, in_waiting_list, color
+                        )
+                        new_booking.save()
+                        if primary_booking is None:
+                            primary_booking = new_booking
+        except IntegrityError as e:
+            if 'tstzrange_constraint' in str(e):
+                # "optimistic concurrency control", between our availability
+                # check with get_all_slots() and now, new event can have been
+                # created and conflict with the events we want to create, and
+                # so we get an IntegrityError exception. In this case we
+                # restart the fillslot() from the begginning to redo the
+                # availability check and return a proper error to the client.
+                #
+                # To prevent looping, we raise an APIError during the second run
+                # of fillslot().
+                if retry:
+                    raise APIError(N_('no more desk available'))
+                return self.fillslot(request, agenda_identifier=agenda_identifier, slots=slots, retry=True)
+            raise
 
         response = {
             'err': 0,
diff --git a/tests/api/fillslot/test_all.py b/tests/api/fillslot/test_all.py
index 05f09e9a..f678ec87 100644
--- a/tests/api/fillslot/test_all.py
+++ b/tests/api/fillslot/test_all.py
@@ -3,7 +3,7 @@ import urllib.parse as urlparse
 from unittest import mock
 
 import pytest
-from django.db import connection
+from django.db import IntegrityError, connection
 from django.test.utils import CaptureQueriesContext
 from django.utils.timezone import localtime, now
 
@@ -172,6 +172,44 @@ def test_booking_api(app, user):
     resp = app.post('/api/agenda/0/fillslot/%s/' % event.id, status=404)
 
 
+def test_booking_api_event_exclusion_constraint(app, user):
+    agenda = Agenda.objects.create(label='Foo bar', kind='meetings')
+    meeting_type = MeetingType.objects.create(agenda=agenda, slug='foo-bar')
+    desk = Desk.objects.create(agenda=agenda, slug='desk')
+    tomorrow = now() + datetime.timedelta(days=1)
+    TimePeriod.objects.create(
+        weekday=tomorrow.date().weekday(),
+        start_time=datetime.time(9, 0),
+        end_time=datetime.time(17, 00),
+        desk=desk,
+    )
+    resp = app.get('/api/agenda/meetings/%s/datetimes/' % meeting_type.id)
+    event_id = resp.json['data'][2]['id']
+
+    app.authorization = ('Basic', ('john.doe', 'password'))
+
+    original_save = Event.save
+    global first_call  # pylint: disable=global-variable-undefined
+    first_call = True
+
+    def wrapped(*args, **kwargs):
+        global first_call  # pylint: disable=global-variable-undefined
+        if first_call is True:
+            first_call = False
+            raise IntegrityError('tstzrange_constraint')
+        return original_save(*args, **kwargs)
+
+    with mock.patch('chrono.agendas.models.Event.save', autospec=True) as mock_create:
+        mock_create.side_effect = wrapped
+        resp = app.post_json(
+            '/api/agenda/%s/fillslot/%s/' % (agenda.slug, event_id),
+        )
+        assert len(mock_create.call_args_list) == 2
+        assert resp.json['err'] == 0
+        assert Event.objects.count() == 1
+        assert Booking.objects.count() == 1
+
+
 def test_booking_api_extra_emails(app, user):
     agenda = Agenda.objects.create(label='Foo bar', kind='events')
     event = Event.objects.create(