diff --git a/golem_activity_registration_slot/models/golem_activity_registration.py b/golem_activity_registration_slot/models/golem_activity_registration.py
index 077dc43..12d8bb0 100644
--- a/golem_activity_registration_slot/models/golem_activity_registration.py
+++ b/golem_activity_registration_slot/models/golem_activity_registration.py
@@ -30,11 +30,16 @@ class GolemActivityRegistration(models.Model):
         """ Create registration slot """
         reg = super(GolemActivityRegistration, self).create(vals)
         if reg.activity_id.individual_slots:
-            slots = self.env['golem.activity.registration.slot'].search([], order='hour_stop')
+            slots = self.env['golem.activity.registration.slot'].search(
+                [('activity_id', '=', reg.activity_id.id)], order='hour_stop')
+            if len(slots) >= reg.activity_id.slots_number:
+                verr = _(u'No available slot to register in this activity')
+                raise ValidationError(verr)
+            hour_start = slots[-1].hour_stop if slots else reg.activity_id.hour_start
             self.env['golem.activity.registration.slot'].create({
                 'activity_id': reg.activity_id.id,
                 'member_id': reg.member_id.id,
-                'hour_start': slots[-1].hour_stop,
-                'hour_stop': slots[-1].hour_stop + reg.activity_id.slots_duration
+                'hour_start': hour_start,
+                'hour_stop': hour_start + reg.activity_id.slots_duration
             })
         return reg