diff --git a/src/pretix/base/services/cart.py b/src/pretix/base/services/cart.py
index 2387f988e..a3e7b7f09 100644
--- a/src/pretix/base/services/cart.py
+++ b/src/pretix/base/services/cart.py
@@ -74,6 +74,7 @@ from pretix.base.services.tasks import ProfiledEventTask
 from pretix.base.settings import PERSON_NAME_SCHEMES, LazyI18nStringList
 from pretix.base.signals import validate_cart_addons
 from pretix.base.templatetags.rich_text import rich_text
+from pretix.base.timemachine import time_machine_now, time_machine_now_assigned
 from pretix.celery_app import app
 from pretix.presale.signals import (
     checkout_confirm_messages, fee_calculation_for_cart,
@@ -278,7 +279,7 @@ class CartManager:
                  sales_channel='web'):
         self.event = event
         self.cart_id = cart_id
-        self.now_dt = now()
+        self.real_now_dt = now()
         self._operations = []
         self._quota_diff = Counter()
         self._voucher_use_diff = Counter()
@@ -305,10 +306,10 @@ class CartManager:
         return self._seated_cache[item, subevent]
 
     def _calculate_expiry(self):
-        self._expiry = self.now_dt + timedelta(minutes=self.event.settings.get('reservation_time', as_type=int))
+        self._expiry = self.real_now_dt + timedelta(minutes=self.event.settings.get('reservation_time', as_type=int))
 
     def _check_presale_dates(self):
-        if self.event.presale_start and self.now_dt < self.event.presale_start:
+        if self.event.presale_start and time_machine_now(self.real_now_dt) < self.event.presale_start:
             raise CartError(error_messages['not_started'])
         if self.event.presale_has_ended:
             raise CartError(error_messages['ended'])
@@ -319,13 +320,13 @@ class CartManager:
                     tlv.datetime(self.event).date(),
                     time(hour=23, minute=59, second=59)
                 ), self.event.timezone)
-                if term_last < self.now_dt:
+                if term_last < time_machine_now(self.real_now_dt):
                     raise CartError(error_messages['payment_ended'])
 
     def _extend_expiry_of_valid_existing_positions(self):
         # Extend this user's cart session to ensure all items in the cart expire at the same time
         # We can extend the reservation of items which are not yet expired without risk
-        self.positions.filter(expires__gt=self.now_dt).update(expires=self._expiry)
+        self.positions.filter(expires__gt=self.real_now_dt).update(expires=self._expiry)
 
     def _delete_out_of_timeframe(self):
         err = None
@@ -333,12 +334,12 @@ class CartManager:
             if not cp.pk:
                 continue
 
-            if cp.subevent and cp.subevent.presale_start and self.now_dt < cp.subevent.presale_start:
+            if cp.subevent and cp.subevent.presale_start and time_machine_now(self.real_now_dt) < cp.subevent.presale_start:
                 err = error_messages['some_subevent_not_started']
                 cp.addons.all().delete()
                 cp.delete()
 
-            if cp.subevent and cp.subevent.presale_end and self.now_dt > cp.subevent.presale_end:
+            if cp.subevent and cp.subevent.presale_end and time_machine_now(self.real_now_dt) > cp.subevent.presale_end:
                 err = error_messages['some_subevent_ended']
                 cp.addons.all().delete()
                 cp.delete()
@@ -350,7 +351,7 @@ class CartManager:
                         tlv.datetime(cp.subevent).date(),
                         time(hour=23, minute=59, second=59)
                     ), self.event.timezone)
-                    if term_last < self.now_dt:
+                    if term_last < time_machine_now(self.real_now_dt):
                         err = error_messages['some_subevent_ended']
                         cp.addons.all().delete()
                         cp.delete()
@@ -449,7 +450,7 @@ class CartManager:
             if op.subevent and not op.subevent.active:
                 raise CartError(error_messages['inactive_subevent'])
 
-            if op.subevent and op.subevent.presale_start and self.now_dt < op.subevent.presale_start:
+            if op.subevent and op.subevent.presale_start and time_machine_now(self.real_now_dt) < op.subevent.presale_start:
                 raise CartError(error_messages['not_started'])
 
             if op.subevent and op.subevent.presale_has_ended:
@@ -472,7 +473,7 @@ class CartManager:
                         tlv.datetime(op.subevent).date(),
                         time(hour=23, minute=59, second=59)
                     ), self.event.timezone)
-                    if term_last < self.now_dt:
+                    if term_last < time_machine_now(self.real_now_dt):
                         raise CartError(error_messages['payment_ended'])
 
         if isinstance(op, self.AddOperation):
@@ -509,7 +510,7 @@ class CartManager:
         )
         if not self.event.settings.seating_choice:
             requires_seat = Value(0, output_field=IntegerField())
-        expired = self.positions.filter(expires__lte=self.now_dt).select_related(
+        expired = self.positions.filter(expires__lte=self.real_now_dt).select_related(
             'item', 'variation', 'voucher', 'addon_to', 'addon_to__item'
         ).annotate(
             requires_seat=requires_seat
@@ -690,7 +691,7 @@ class CartManager:
                         # than either of the possible default assumptions.
                         predicted_redeemed_after = (
                             voucher.redeemed +
-                            CartPosition.objects.filter(voucher=voucher, expires__gte=self.now_dt).count() +
+                            CartPosition.objects.filter(voucher=voucher, expires__gte=self.real_now_dt).count() +
                             self._voucher_use_diff[voucher] +
                             voucher_use_diff[voucher]
                         )
@@ -982,7 +983,7 @@ class CartManager:
                 current_num = len(current_addons[cp].get(k, []))
                 if input_num < current_num:
                     for a in current_addons[cp][k][:current_num - input_num]:
-                        if a.expires > self.now_dt:
+                        if a.expires > self.real_now_dt:
                             quotas = list(a.quotas)
 
                             for quota in quotas:
@@ -996,7 +997,7 @@ class CartManager:
 
     def _get_voucher_availability(self):
         vouchers_ok, self._voucher_depend_on_cart = _get_voucher_availability(
-            self.event, self._voucher_use_diff, self.now_dt,
+            self.event, self._voucher_use_diff, self.real_now_dt,
             exclude_position_ids=[
                 op.position.id for op in self._operations if isinstance(op, self.ExtendOperation)
             ]
@@ -1101,7 +1102,7 @@ class CartManager:
                 shared_lock_objects=[self.event]
             )
         vouchers_ok = self._get_voucher_availability()
-        quotas_ok = _get_quota_availability(self._quota_diff, self.now_dt)
+        quotas_ok = _get_quota_availability(self._quota_diff, self.real_now_dt)
         err = None
         new_cart_positions = []
         deleted_positions = set()
@@ -1118,7 +1119,7 @@ class CartManager:
 
         for iop, op in enumerate(self._operations):
             if isinstance(op, self.RemoveOperation):
-                if op.position.expires > self.now_dt:
+                if op.position.expires > self.real_now_dt:
                     for q in op.position.quotas:
                         quotas_ok[q] += 1
                 addons = op.position.addons.all()
@@ -1395,7 +1396,7 @@ class CartManager:
         err = self.extend_expired_positions() or err
         err = err or self._check_min_per_voucher()
 
-        self.now_dt = now()
+        self.real_now_dt = now()
 
         self._extend_expiry_of_valid_existing_positions()
         err = self._perform_operations() or err
@@ -1487,7 +1488,7 @@ def get_fees(event, request, total, invoice_address, payments, positions):
 
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
 def add_items_to_cart(self, event: int, items: List[dict], cart_id: str=None, locale='en',
-                      invoice_address: int=None, widget_data=None, sales_channel='web') -> None:
+                      invoice_address: int=None, widget_data=None, sales_channel='web', override_now_dt: datetime=None) -> None:
     """
     Adds a list of items to a user's cart.
     :param event: The event ID in question
@@ -1495,7 +1496,7 @@ def add_items_to_cart(self, event: int, items: List[dict], cart_id: str=None, lo
     :param cart_id: Session ID of a guest
     :raises CartError: On any error that occurred
     """
-    with language(locale):
+    with language(locale), time_machine_now_assigned(override_now_dt):
         ia = False
         if invoice_address:
             try:
@@ -1517,14 +1518,14 @@ def add_items_to_cart(self, event: int, items: List[dict], cart_id: str=None, lo
 
 
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
-def apply_voucher(self, event: Event, voucher: str, cart_id: str=None, locale='en', sales_channel='web') -> None:
+def apply_voucher(self, event: Event, voucher: str, cart_id: str=None, locale='en', sales_channel='web', override_now_dt: datetime=None) -> None:
     """
     Removes a list of items from a user's cart.
     :param event: The event ID in question
     :param voucher: A voucher code
     :param session: Session ID of a guest
     """
-    with language(locale):
+    with language(locale), time_machine_now_assigned(override_now_dt):
         try:
             try:
                 cm = CartManager(event=event, cart_id=cart_id, sales_channel=sales_channel)
@@ -1537,14 +1538,14 @@ def apply_voucher(self, event: Event, voucher: str, cart_id: str=None, locale='e
 
 
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
-def remove_cart_position(self, event: Event, position: int, cart_id: str=None, locale='en', sales_channel='web') -> None:
+def remove_cart_position(self, event: Event, position: int, cart_id: str=None, locale='en', sales_channel='web', override_now_dt: datetime=None) -> None:
     """
     Removes a list of items from a user's cart.
     :param event: The event ID in question
     :param position: A cart position ID
     :param session: Session ID of a guest
     """
-    with language(locale):
+    with language(locale), time_machine_now_assigned(override_now_dt):
         try:
             try:
                 cm = CartManager(event=event, cart_id=cart_id, sales_channel=sales_channel)
@@ -1557,13 +1558,13 @@ def remove_cart_position(self, event: Event, position: int, cart_id: str=None, l
 
 
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
-def clear_cart(self, event: Event, cart_id: str=None, locale='en', sales_channel='web') -> None:
+def clear_cart(self, event: Event, cart_id: str=None, locale='en', sales_channel='web', override_now_dt: datetime=None) -> None:
     """
     Removes a list of items from a user's cart.
     :param event: The event ID in question
     :param session: Session ID of a guest
     """
-    with language(locale):
+    with language(locale), time_machine_now_assigned(override_now_dt):
         try:
             try:
                 cm = CartManager(event=event, cart_id=cart_id, sales_channel=sales_channel)
@@ -1577,14 +1578,14 @@ def clear_cart(self, event: Event, cart_id: str=None, locale='en', sales_channel
 
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
 def set_cart_addons(self, event: Event, addons: List[dict], cart_id: str=None, locale='en',
-                    invoice_address: int=None, sales_channel='web') -> None:
+                    invoice_address: int=None, sales_channel='web', override_now_dt: datetime=None) -> None:
     """
     Removes a list of items from a user's cart.
     :param event: The event ID in question
     :param addons: A list of dicts with the keys addon_to, item, variation
     :param session: Session ID of a guest
     """
-    with language(locale):
+    with language(locale), time_machine_now_assigned(override_now_dt):
         ia = False
         if invoice_address:
             try:
diff --git a/src/pretix/base/services/orders.py b/src/pretix/base/services/orders.py
index a52cc541a..566792938 100644
--- a/src/pretix/base/services/orders.py
+++ b/src/pretix/base/services/orders.py
@@ -102,7 +102,7 @@ from pretix.base.signals import (
     order_fee_calculation, order_paid, order_placed, order_split,
     order_valid_if_pending, periodic_task, validate_order,
 )
-from pretix.base.timemachine import time_machine_now
+from pretix.base.timemachine import time_machine_now, time_machine_now_assigned
 from pretix.celery_app import app
 from pretix.helpers import OF_SELF
 from pretix.helpers.models import modelcopy
@@ -2853,8 +2853,8 @@ class OrderChangeManager:
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(OrderError,))
 def perform_order(self, event: Event, payments: List[dict], positions: List[str],
                   email: str=None, locale: str=None, address: int=None, meta_info: dict=None,
-                  sales_channel: str='web', shown_total=None, customer=None):
-    with language(locale):
+                  sales_channel: str='web', shown_total=None, customer=None, override_now_dt: datetime=None):
+    with language(locale), time_machine_now_assigned(override_now_dt):
         try:
             try:
                 return _perform_order(event, payments, positions, email, locale, address, meta_info,
diff --git a/src/pretix/base/timemachine.py b/src/pretix/base/timemachine.py
index c1f12b6cd..56f76bc77 100644
--- a/src/pretix/base/timemachine.py
+++ b/src/pretix/base/timemachine.py
@@ -33,6 +33,7 @@
 # License for the specific language governing permissions and limitations under the License.
 
 import threading
+from contextlib import contextmanager
 
 from dateutil.parser import parse
 from django.utils.timezone import now
@@ -64,5 +65,16 @@ class TimeMachineMiddleware:
             TimeMachineMiddleware.tls.now_dt = None
 
 
-def time_machine_now(now_dt=None):
-    return getattr(TimeMachineMiddleware.tls, 'now_dt', None) or now_dt or now()
+def time_machine_now(default=False):
+    if default is False:
+        default = now()
+    return getattr(TimeMachineMiddleware.tls, 'now_dt', None) or default
+
+
+@contextmanager
+def time_machine_now_assigned(now_dt):
+    try:
+        TimeMachineMiddleware.tls.now_dt = now_dt
+        yield
+    finally:
+        TimeMachineMiddleware.tls.now_dt = None
diff --git a/src/pretix/presale/checkoutflow.py b/src/pretix/presale/checkoutflow.py
index 622e2b4bc..4e8514334 100644
--- a/src/pretix/presale/checkoutflow.py
+++ b/src/pretix/presale/checkoutflow.py
@@ -73,6 +73,7 @@ from pretix.base.signals import validate_cart_addons
 from pretix.base.templatetags.money import money_filter
 from pretix.base.templatetags.phone_format import phone_format
 from pretix.base.templatetags.rich_text import rich_text_snippet
+from pretix.base.timemachine import time_machine_now
 from pretix.base.views.tasks import AsyncAction
 from pretix.celery_app import app
 from pretix.helpers.http import redirect_to_url
@@ -706,7 +707,7 @@ class AddOnsStep(CartMixin, AsyncAction, TemplateFlowStep):
 
         return self.do(self.request.event.id, data, get_or_create_cart_id(self.request),
                        invoice_address=self.invoice_address.pk, locale=get_language(),
-                       sales_channel=request.sales_channel.identifier)
+                       sales_channel=request.sales_channel.identifier, override_now_dt=time_machine_now(default=None))
 
 
 class QuestionsStep(QuestionsViewMixin, CartMixin, TemplateFlowStep):
@@ -1548,6 +1549,7 @@ class ConfirmStep(CartMixin, AsyncAction, TemplateFlowStep):
             sales_channel=request.sales_channel.identifier,
             shown_total=self.cart_session.get('shown_total'),
             customer=self.cart_session.get('customer'),
+            override_now_dt=time_machine_now(default=None),
         )
 
     def get_success_message(self, value):
diff --git a/src/pretix/presale/views/cart.py b/src/pretix/presale/views/cart.py
index c9b296843..92c188056 100644
--- a/src/pretix/presale/views/cart.py
+++ b/src/pretix/presale/views/cart.py
@@ -63,6 +63,7 @@ from pretix.base.services.cart import (
     CartError, add_items_to_cart, apply_voucher, clear_cart, error_messages,
     remove_cart_position,
 )
+from pretix.base.timemachine import time_machine_now
 from pretix.base.views.tasks import AsyncAction
 from pretix.helpers.http import redirect_to_url
 from pretix.multidomain.urlreverse import eventreverse
@@ -429,7 +430,8 @@ class CartApplyVoucher(EventViewMixin, CartActionMixin, AsyncAction, View):
     def post(self, request, *args, **kwargs):
         if 'voucher' in request.POST:
             return self.do(self.request.event.id, request.POST.get('voucher'), get_or_create_cart_id(self.request),
-                           translation.get_language(), request.sales_channel.identifier)
+                           translation.get_language(), request.sales_channel.identifier,
+                           time_machine_now(default=None))
         else:
             if 'ajax' in self.request.GET or 'ajax' in self.request.POST:
                 return JsonResponse({
@@ -455,7 +457,8 @@ class CartRemove(EventViewMixin, CartActionMixin, AsyncAction, View):
         if 'id' in request.POST:
             try:
                 return self.do(self.request.event.id, int(request.POST.get('id')), get_or_create_cart_id(self.request),
-                               translation.get_language(), request.sales_channel.identifier)
+                               translation.get_language(), request.sales_channel.identifier,
+                               time_machine_now(default=None))
             except ValueError:
                 return redirect_to_url(self.get_error_url())
         else:
@@ -478,7 +481,7 @@ class CartClear(EventViewMixin, CartActionMixin, AsyncAction, View):
 
     def post(self, request, *args, **kwargs):
         return self.do(self.request.event.id, get_or_create_cart_id(self.request), translation.get_language(),
-                       request.sales_channel.identifier)
+                       request.sales_channel.identifier, time_machine_now(default=None))
 
 
 @method_decorator(allow_cors_if_namespaced, 'dispatch')
@@ -534,7 +537,8 @@ class CartAdd(EventViewMixin, CartActionMixin, AsyncAction, View):
         items = self._items_from_post_data()
         if items:
             return self.do(self.request.event.id, items, cart_id, translation.get_language(),
-                           self.invoice_address.pk, widget_data, self.request.sales_channel.identifier)
+                           self.invoice_address.pk, widget_data, self.request.sales_channel.identifier,
+                           time_machine_now(default=None))
         else:
             if 'ajax' in self.request.GET or 'ajax' in self.request.POST:
                 return JsonResponse({
diff --git a/src/tests/presale/test_cart.py b/src/tests/presale/test_cart.py
index 57f54b1d7..44bfaf795 100644
--- a/src/tests/presale/test_cart.py
+++ b/src/tests/presale/test_cart.py
@@ -49,7 +49,7 @@ from pretix.base.decimal import round_decimal
 from pretix.base.models import (
     CartPosition, Discount, Event, InvoiceAddress, Item, ItemCategory,
     ItemVariation, Organizer, Question, QuestionAnswer, Quota, SeatingPlan,
-    Voucher,
+    Team, User, Voucher,
 )
 from pretix.base.models.items import (
     ItemAddOn, ItemBundle, SubEventItem, SubEventItemVariation,
@@ -4274,3 +4274,101 @@ class CartSeatingTest(CartTestMixin, TestCase):
             self.cm.commit()
 
         assert not CartPosition.objects.filter(cart_id=self.session_key).exists()
+
+
+class CartTimemachineTest(CartTestMixin, TestCase):
+    @scopes_disabled()
+    def setUp(self):
+        super().setUp()
+        self.user = User.objects.create_user('dummy@dummy.dummy', 'dummy')
+        self.team1 = Team.objects.create(organizer=self.orga, can_create_events=True, can_change_event_settings=True,
+                                         can_change_items=True, all_events=True)
+        self.team1.members.add(self.user)
+        self.client.login(email='dummy@dummy.dummy', password='dummy')
+
+    def _set_time_machine_now(self, dt):
+        session = self.client.session
+        session['timemachine_now_dt'] = str(dt)
+        session.save()
+
+    def test_before_presale_timemachine(self):
+        self.event.presale_start = now() + timedelta(days=1)
+        self.event.testmode = True
+        self.event.save()
+        self._set_time_machine_now(now() + timedelta(days=2))
+
+        response = self.client.post('/%s/%s/cart/add' % (self.orga.slug, self.event.slug), {
+            'item_%d' % self.ticket.id: '1'
+        }, follow=True)
+        self.assertRedirects(response, '/%s/%s/?require_cookie=true' % (self.orga.slug, self.event.slug),
+                             target_status_code=200)
+        assert 'alert-success' in response.rendered_content
+        with scopes_disabled():
+            objs = list(CartPosition.objects.filter(cart_id=self.session_key, event=self.event))
+        self.assertEqual(len(objs), 1)
+        self.assertEqual(objs[0].item, self.ticket)
+        self.assertIsNone(objs[0].variation)
+        self.assertEqual(objs[0].price, 23)
+        self.assertLessEqual(objs[0].expires, now() + timedelta(
+            minutes=self.event.settings.get('reservation_time', as_type=int)))
+
+    def test_after_presale_timemachine(self):
+        self.event.presale_end = now() - timedelta(days=1)
+        self.event.testmode = True
+        self.event.save()
+        self._set_time_machine_now(now() - timedelta(days=2))
+
+        response = self.client.post('/%s/%s/cart/add' % (self.orga.slug, self.event.slug), {
+            'item_%d' % self.ticket.id: '1'
+        }, follow=True)
+        self.assertRedirects(response, '/%s/%s/?require_cookie=true' % (self.orga.slug, self.event.slug),
+                             target_status_code=200)
+        assert 'alert-success' in response.rendered_content
+        with scopes_disabled():
+            objs = list(CartPosition.objects.filter(cart_id=self.session_key, event=self.event))
+        self.assertEqual(len(objs), 1)
+        self.assertEqual(objs[0].item, self.ticket)
+        self.assertIsNone(objs[0].variation)
+        self.assertEqual(objs[0].price, 23)
+        self.assertLessEqual(objs[0].expires, now() + timedelta(
+            minutes=self.event.settings.get('reservation_time', as_type=int)))
+
+    def test_not_yet_available_with_timemachine_in_time(self):
+        self.event.testmode = True
+        self.event.save()
+        self.ticket.available_from = now() + timedelta(days=2)
+        self.ticket.available_until = now() + timedelta(days=4)
+        self.ticket.save()
+        self._set_time_machine_now(now() + timedelta(days=3))
+        self.client.post('/%s/%s/cart/add' % (self.orga.slug, self.event.slug), {
+            'item_%d' % self.ticket.id: '1',
+        }, follow=True)
+        with scopes_disabled():
+            self.assertEqual(CartPosition.objects.filter(cart_id=self.session_key, event=self.event).count(), 1)
+
+    def test_variation_no_longer_available_with_timemachine_in_time(self):
+        self.event.testmode = True
+        self.event.save()
+        self.shirt_blue.available_from = now() - timedelta(days=4)
+        self.shirt_blue.available_until = now() - timedelta(days=2)
+        self.shirt_blue.save()
+        self._set_time_machine_now(now() - timedelta(days=3))
+
+        self.client.post('/%s/%s/cart/add' % (self.orga.slug, self.event.slug), {
+            'variation_%d_%d' % (self.shirt.id, self.shirt_blue.id): '1',
+        }, follow=True)
+        with scopes_disabled():
+            self.assertEqual(CartPosition.objects.filter(cart_id=self.session_key, event=self.event).count(), 1)
+
+    def test_variation_no_longer_available_with_timemachine_before(self):
+        self.event.testmode = True
+        self.event.save()
+        self.shirt_blue.available_from = now() - timedelta(days=4)
+        self.shirt_blue.available_until = now() - timedelta(days=2)
+        self.shirt_blue.save()
+        self._set_time_machine_now(now() - timedelta(days=5))
+        self.client.post('/%s/%s/cart/add' % (self.orga.slug, self.event.slug), {
+            'variation_%d_%d' % (self.shirt.id, self.shirt_blue.id): '1',
+        }, follow=True)
+        with scopes_disabled():
+            self.assertEqual(CartPosition.objects.filter(cart_id=self.session_key, event=self.event).count(), 0)