diff --git a/src/pretix/control/context.py b/src/pretix/control/context.py
index be369677eb..30d15f988d 100644
--- a/src/pretix/control/context.py
+++ b/src/pretix/control/context.py
@@ -155,7 +155,7 @@ def _default_context(request):
         if not gs.settings.update_check_ack and 'runserver' not in sys.argv:
             ctx['warning_update_check_active'] = True
 
-    ctx['ie_deprecation_warning'] = 'MSIE' in request.headers['User-Agent'] or 'Trident/' in request.headers['User-Agent']
+    ctx['ie_deprecation_warning'] = 'MSIE' in request.headers.get('User-Agent', '') or 'Trident/' in request.headers.get('User-Agent', '')
 
     if request.user.is_authenticated:
         ctx['staff_session'] = request.user.has_active_staff_session(request.session.session_key)