diff --git a/arkindex/documents/serializers/light.py b/arkindex/documents/serializers/light.py
index d7219922451a912239032a01767da43a9503cf29..ce516f2480fec66eeb92745454a4fe84b962fe69 100644
--- a/arkindex/documents/serializers/light.py
+++ b/arkindex/documents/serializers/light.py
@@ -84,8 +84,8 @@ class ElementTypeLightSerializer(serializers.ModelSerializer):
     def validate(self, data):
         slug = data.get('slug') if 'slug' in data else self.instance.slug
         corpus = data.get('corpus') if 'corpus' in data else self.instance.corpus
-        type = corpus.types.filter(slug=slug)
-        if type.exists() and (not self.instance or type.first().id != self.instance.id):
+        type = corpus.types.filter(slug=slug).using('default').first()
+        if type is not None and (not self.instance or type.id != self.instance.id):
             raise ValidationError({'slug': ['Slug must be unique']})
         return data