diff --git a/lib/adamantium/micropub_request_parser.rb b/lib/adamantium/micropub_request_parser.rb
index b5e0f72..c63c005 100644
--- a/lib/adamantium/micropub_request_parser.rb
+++ b/lib/adamantium/micropub_request_parser.rb
@@ -100,7 +100,7 @@ module Adamantium
       new_params[:slug] = SecureRandom.uuid
       new_params[:category] = params.dig(:properties, :category)
       published = DateTime.parse(params.dig(:properties, :published)&.first).new_offset(0)
-      new_params[:published_at] = published
+      new_params[:published_at] = published.to_s
       new_params[:post_type] = :checkin
       location = params.dig(:properties, :location).first[:properties]
       new_params[:photos] = []