diff --git a/src/pretix/control/forms/subevents.py b/src/pretix/control/forms/subevents.py
index 6c3145d90..474d731bc 100644
--- a/src/pretix/control/forms/subevents.py
+++ b/src/pretix/control/forms/subevents.py
@@ -463,6 +463,7 @@ class RRuleFormSetForm(RRuleForm):
 
 RRuleFormSet = formset_factory(
     RRuleFormSetForm,
+    min_num=1, validate_min=True,
     can_order=False, can_delete=True, extra=1
 )