diff --git a/app/models/activity.rb b/app/models/activity.rb
index 632db7da4..58d7004a1 100644
--- a/app/models/activity.rb
+++ b/app/models/activity.rb
@@ -168,7 +168,7 @@ def as_indexed_json(options={})
       "request_uuid" => request_uuid,
       "changes" => changes,
       "created" => created,
-      "doi" => doi.as_indexed_json
+      "doi" => doi.present? ? doi.as_indexed_json : nil
     }
   end