diff --git a/sdbs_pile/pile/admin.py b/sdbs_pile/pile/admin.py
index 0646951..92c484a 100644
--- a/sdbs_pile/pile/admin.py
+++ b/sdbs_pile/pile/admin.py
@@ -33,7 +33,7 @@ class DocumentExternalListFilter(admin.SimpleListFilter):
 
 
 class DocumentAdminForm(forms.ModelForm):
-    related = forms.ModelMultipleChoiceField(queryset=Document.objects.none())
+    related = forms.ModelMultipleChoiceField(queryset=Document.objects.none(), required=False)
 
     class Meta:
         model = Document