diff --git a/src/pretix/control/forms/event.py b/src/pretix/control/forms/event.py
index 2fba6775ff..95d036f630 100644
--- a/src/pretix/control/forms/event.py
+++ b/src/pretix/control/forms/event.py
@@ -145,7 +145,7 @@ class EventWizardBasicsForm(I18nModelForm):
 
     def clean_slug(self):
         slug = self.cleaned_data['slug']
-        if Event.objects.filter(slug=slug, organizer=self.organizer).exists():
+        if Event.objects.filter(slug__iexact=slug, organizer=self.organizer).exists():
             raise forms.ValidationError(
                 self.error_messages['duplicate_slug'],
                 code='duplicate_slug'
diff --git a/src/pretix/control/forms/organizer.py b/src/pretix/control/forms/organizer.py
index a2dd5b4b8e..ababf1a820 100644
--- a/src/pretix/control/forms/organizer.py
+++ b/src/pretix/control/forms/organizer.py
@@ -23,7 +23,7 @@ class OrganizerForm(I18nModelForm):
 
     def clean_slug(self):
         slug = self.cleaned_data['slug']
-        if Organizer.objects.filter(slug=slug).exists():
+        if Organizer.objects.filter(slug__iexact=slug).exists():
             raise forms.ValidationError(
                 self.error_messages['duplicate_slug'],
                 code='duplicate_slug',