diff --git a/src/pretix/base/timemachine.py b/src/pretix/base/timemachine.py
index c8ba4c2c21..b25804504a 100644
--- a/src/pretix/base/timemachine.py
+++ b/src/pretix/base/timemachine.py
@@ -21,9 +21,11 @@
 #
 import contextvars
 from contextlib import contextmanager
+from datetime import datetime
 
-from dateutil.parser import parse
+from django.contrib import messages
 from django.utils.timezone import now
+from django.utils.translation import gettext_lazy as _
 
 from pretix.base.auth import has_event_access_permission
 
@@ -34,8 +36,17 @@ timemachine_now_var = contextvars.ContextVar('timemachine_now', default=None)
 def time_machine_now_assigned_from_request(request):
     if hasattr(request, 'event') and f'timemachine_now_dt:{request.event.pk}' in request.session and \
             request.event.testmode and has_event_access_permission(request):
-        request.now_dt = parse(request.session[f'timemachine_now_dt:{request.event.pk}'])
-        request.now_dt_is_fake = True
+        try:
+            request.now_dt = datetime.fromisoformat(request.session[f'timemachine_now_dt:{request.event.pk}'])
+            request.now_dt_is_fake = True
+        except ValueError:
+            del request.session[f'timemachine_now_dt:{request.event.pk}']
+            messages.error(
+                request, _('Invalid date.')
+            )
+            request.now_dt = now()
+            request.now_dt_is_fake = False
+
     else:
         request.now_dt = now()
         request.now_dt_is_fake = False
diff --git a/src/pretix/presale/views/event.py b/src/pretix/presale/views/event.py
index fe54f21eb8..17faa5b8e6 100644
--- a/src/pretix/presale/views/event.py
+++ b/src/pretix/presale/views/event.py
@@ -41,7 +41,6 @@ from importlib import import_module
 from urllib.parse import urlencode
 
 import isoweek
-from dateutil import parser
 from django import forms
 from django.conf import settings
 from django.contrib import messages
@@ -603,12 +602,17 @@ class EventTimeMachine(EventViewMixin, TemplateView):
             raise PermissionDenied(_('You are not allowed to access time machine mode.'))
         if not request.event.testmode:
             raise PermissionDenied(_('This feature is only available in test mode.'))
+
+        initial = {}
+        if request.session.get(f'timemachine_now_dt:{request.event.pk}', None):
+            try:
+                initial['now_dt'] = datetime.fromisoformat(request.session.get(f'timemachine_now_dt:{request.event.pk}', None))
+            except ValueError:
+                pass
+
         self.timemachine_form = TimemachineForm(
             data=request.method == 'POST' and request.POST or None,
-            initial=(
-                {'now_dt': parser.parse(request.session.get(f'timemachine_now_dt:{request.event.pk}', None))}
-                if request.session.get(f'timemachine_now_dt:{request.event.pk}', None) else {}
-            )
+            initial=initial
         )
 
     def get_context_data(self, **kwargs):
@@ -622,7 +626,7 @@ class EventTimeMachine(EventViewMixin, TemplateView):
             messages.success(self.request, _('Time machine disabled!'))
             return redirect(self.get_success_url())
         elif self.timemachine_form.is_valid():
-            request.session[f'timemachine_now_dt:{request.event.pk}'] = str(self.timemachine_form.cleaned_data['now_dt'])
+            request.session[f'timemachine_now_dt:{request.event.pk}'] = self.timemachine_form.cleaned_data['now_dt'].isoformat()
             return redirect(eventreverse(request.event, "presale:event.index"))
         else:
             return self.get(request)