diff --git a/app/controllers/media_proxy_controller.rb b/app/controllers/media_proxy_controller.rb
index 155670837eb74098a7de56bf5ee9be4f5b9f4646..d820b257e0ac65605776c7dc7f3f3a30b50db9af 100644
--- a/app/controllers/media_proxy_controller.rb
+++ b/app/controllers/media_proxy_controller.rb
@@ -8,6 +8,8 @@ class MediaProxyController < ApplicationController
       if lock.acquired?
         @media_attachment = MediaAttachment.remote.find(params[:id])
         redownload! if @media_attachment.needs_redownload? && !reject_media?
+      else
+        raise Mastodon::RaceConditionError
       end
     end
 
diff --git a/app/lib/activitypub/activity/create.rb b/app/lib/activitypub/activity/create.rb
index 8d17a4ebe2e8efb99be6e50b84a8a03ec1c3d7c2..ab1d63cd496e11a38cce0d53cdc085c370e8ee05 100644
--- a/app/lib/activitypub/activity/create.rb
+++ b/app/lib/activitypub/activity/create.rb
@@ -11,6 +11,8 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
       if lock.acquired?
         @status = find_existing_status
         process_status if @status.nil?
+      else
+        raise Mastodon::RaceConditionError
       end
     end
 
diff --git a/app/lib/ostatus/activity/creation.rb b/app/lib/ostatus/activity/creation.rb
index dbccc83302953382571e40246ca64c936799b334..d3a303a0c4896f23edeaf68db9a7ab77f622c4a0 100644
--- a/app/lib/ostatus/activity/creation.rb
+++ b/app/lib/ostatus/activity/creation.rb
@@ -15,6 +15,8 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
         @status = find_status(id)
         return [@status, false] unless @status.nil?
         @status = process_status
+      else
+        raise Mastodon::RaceConditionError
       end
     end
 
diff --git a/app/services/activitypub/process_account_service.rb b/app/services/activitypub/process_account_service.rb
index 783bbd8e57548e9d510c29716f3bae2429cc24aa..453253db40502a3341c2e23f671aa720fbccc62c 100644
--- a/app/services/activitypub/process_account_service.rb
+++ b/app/services/activitypub/process_account_service.rb
@@ -23,6 +23,8 @@ class ActivityPub::ProcessAccountService < BaseService
         create_account if @account.nil?
         update_account
         process_tags
+      else
+        raise Mastodon::RaceConditionError
       end
     end
 
diff --git a/app/services/fetch_link_card_service.rb b/app/services/fetch_link_card_service.rb
index f9b1b2f0c63b3d1298abb08cb31410d29f12a1b9..86d0f9971dcd79758cb52afd5c376c9503f5d295 100644
--- a/app/services/fetch_link_card_service.rb
+++ b/app/services/fetch_link_card_service.rb
@@ -23,6 +23,8 @@ class FetchLinkCardService < BaseService
       if lock.acquired?
         @card = PreviewCard.find_by(url: @url)
         process_url if @card.nil? || @card.updated_at <= 2.weeks.ago
+      else
+        raise Mastodon::RaceConditionError
       end
     end
 
diff --git a/app/services/resolve_account_service.rb b/app/services/resolve_account_service.rb
index de8d1151d39790a89dd7097e99402f162ffbf876..4323e7f06d57f77c8fe37a618ba463a7faddf3c8 100644
--- a/app/services/resolve_account_service.rb
+++ b/app/services/resolve_account_service.rb
@@ -49,6 +49,8 @@ class ResolveAccountService < BaseService
         else
           handle_ostatus
         end
+      else
+        raise Mastodon::RaceConditionError
       end
     end