diff --git a/swh/web/api/views/snapshot.py b/swh/web/api/views/snapshot.py
index ec7920aa77e477b3ca52ef692479f9aaf63161b4..954d814bbe696eebd110a64ed506d7e6d8932b77 100644
--- a/swh/web/api/views/snapshot.py
+++ b/swh/web/api/views/snapshot.py
@@ -66,7 +66,7 @@ class SnapshotQuerySerializer(serializers.Serializer):
         min_value=0,
         max_value=snapshot_content_max_size,
     )
-    target_types = TargetTypesField(default="", required=False)
+    target_types = TargetTypesField(default=None, required=False)
 
 
 @api_route(