diff --git a/timesketch/api/v1/resources/timeline.py b/timesketch/api/v1/resources/timeline.py
index 9d1425bc0e..3c81023d44 100644
--- a/timesketch/api/v1/resources/timeline.py
+++ b/timesketch/api/v1/resources/timeline.py
@@ -535,6 +535,7 @@ def post(self):
         return self.to_json(searchindex, status_code=HTTP_STATUS_CODE_CREATED)
 
 
+# TODO(Issue 3200): Research more efficient ways to gather unique fields.
 class TimelineFieldsResource(resources.ResourceMixin, Resource):
     """Resource to retrieve unique fields present in a timeline.