diff --git a/app/lib/ostatus/activity/creation.rb b/app/lib/ostatus/activity/creation.rb
index 1e7f47029..dbccc8330 100644
--- a/app/lib/ostatus/activity/creation.rb
+++ b/app/lib/ostatus/activity/creation.rb
@@ -46,7 +46,8 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
         visibility: visibility_scope,
         conversation: find_or_create_conversation,
         thread: thread? ? find_status(thread.first) || find_activitypub_status(thread.first, thread.second) : nil,
-        media_attachment_ids: media_attachments.map(&:id)
+        media_attachment_ids: media_attachments.map(&:id),
+        sensitive: sensitive?
       )
 
       save_mentions(status)
@@ -105,6 +106,11 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
 
   private
 
+  def sensitive?
+    # OStatus-specific convention (not standard)
+    @xml.xpath('./xmlns:category', xmlns: OStatus::TagManager::XMLNS).any? { |category| category['term'] == 'nsfw' }
+  end
+
   def find_or_create_conversation
     uri = @xml.at_xpath('./ostatus:conversation', ostatus: OStatus::TagManager::OS_XMLNS)&.attribute('ref')&.content
     return if uri.nil?
diff --git a/app/lib/ostatus/atom_serializer.rb b/app/lib/ostatus/atom_serializer.rb
index 7c66f2066..698f2ee22 100644
--- a/app/lib/ostatus/atom_serializer.rb
+++ b/app/lib/ostatus/atom_serializer.rb
@@ -368,6 +368,7 @@ class OStatus::AtomSerializer
       append_element(entry, 'link', nil, rel: :enclosure, type: media.file_content_type, length: media.file_file_size, href: full_asset_url(media.file.url(:original, false)))
     end
 
+    append_element(entry, 'category', nil, term: 'nsfw') if status.sensitive? && status.media_attachments.any?
     append_element(entry, 'mastodon:scope', status.visibility)
 
     status.emojis.each do |emoji|