diff --git a/app/controllers/accounts_controller.rb b/app/controllers/accounts_controller.rb
index c270eb000c4b11adaf356fdab6fd3addbe501734..4dc0a783dda3e5e64a9b5c25aad99bef15ace60d 100644
--- a/app/controllers/accounts_controller.rb
+++ b/app/controllers/accounts_controller.rb
@@ -17,7 +17,7 @@ class AccountsController < ApplicationController
       end
 
       format.json do
-        render json: @account, serializer: ActivityPub::ActorSerializer, adapter: ActivityPub::Adapter
+        render json: @account, serializer: ActivityPub::ActorSerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json'
       end
     end
   end
diff --git a/app/controllers/activitypub/outboxes_controller.rb b/app/controllers/activitypub/outboxes_controller.rb
index 30b91f37021dc7156ba88fe665053e706267bb59..9f97ff6226d67480861a8672cf54f3d41717787a 100644
--- a/app/controllers/activitypub/outboxes_controller.rb
+++ b/app/controllers/activitypub/outboxes_controller.rb
@@ -7,7 +7,7 @@ class ActivityPub::OutboxesController < Api::BaseController
     @statuses = @account.statuses.permitted_for(@account, current_account).paginate_by_max_id(20, params[:max_id], params[:since_id])
     @statuses = cache_collection(@statuses, Status)
 
-    render json: outbox_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter
+    render json: outbox_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json'
   end
 
   private
diff --git a/app/controllers/follower_accounts_controller.rb b/app/controllers/follower_accounts_controller.rb
index 5edb4d67c8a878c0d65fb6c17bb0a22ee9aeb0ca..0e194989790006676d561d9adc4337615583d84c 100644
--- a/app/controllers/follower_accounts_controller.rb
+++ b/app/controllers/follower_accounts_controller.rb
@@ -10,7 +10,7 @@ class FollowerAccountsController < ApplicationController
       format.html
 
       format.json do
-        render json: collection_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter
+        render json: collection_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json'
       end
     end
   end
diff --git a/app/controllers/following_accounts_controller.rb b/app/controllers/following_accounts_controller.rb
index 7cafe5fda50a51ad0493d19230c651936bb608b1..d4593093ff643bcae53b00ca1fb1f2f7b5e23750 100644
--- a/app/controllers/following_accounts_controller.rb
+++ b/app/controllers/following_accounts_controller.rb
@@ -10,7 +10,7 @@ class FollowingAccountsController < ApplicationController
       format.html
 
       format.json do
-        render json: collection_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter
+        render json: collection_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json'
       end
     end
   end
diff --git a/app/controllers/statuses_controller.rb b/app/controllers/statuses_controller.rb
index 0cce2ba23c7818357167af374d3f1bbc5d1feded..aa24f23c944ffde3e73408efcbe260c55e6c0a49 100644
--- a/app/controllers/statuses_controller.rb
+++ b/app/controllers/statuses_controller.rb
@@ -20,13 +20,13 @@ class StatusesController < ApplicationController
       end
 
       format.json do
-        render json: @status, serializer: ActivityPub::NoteSerializer, adapter: ActivityPub::Adapter
+        render json: @status, serializer: ActivityPub::NoteSerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json'
       end
     end
   end
 
   def activity
-    render json: @status, serializer: ActivityPub::ActivitySerializer, adapter: ActivityPub::Adapter
+    render json: @status, serializer: ActivityPub::ActivitySerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json'
   end
 
   private
diff --git a/app/controllers/tags_controller.rb b/app/controllers/tags_controller.rb
index 2cd85e185e51d8a6fe2271eadefa1365891e222d..3001b2ee314c52d616ad718bd6a9799c510207c7 100644
--- a/app/controllers/tags_controller.rb
+++ b/app/controllers/tags_controller.rb
@@ -12,7 +12,7 @@ class TagsController < ApplicationController
       format.html
 
       format.json do
-        render json: collection_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter
+        render json: collection_presenter, serializer: ActivityPub::CollectionSerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json'
       end
     end
   end
diff --git a/config/initializers/mime_types.rb b/config/initializers/mime_types.rb
index 30e91ad63f5800bcc85bb4c19336f9b97ca2e4e9..58a6c0063eca19f43177a4ed402c7f5003e1e317 100644
--- a/config/initializers/mime_types.rb
+++ b/config/initializers/mime_types.rb
@@ -1,4 +1,4 @@
 # Be sure to restart your server when you modify this file.
 
-Mime::Type.register 'application/json', :json, %w(text/x-json application/jsonrequest application/jrd+json application/activity+json)
+Mime::Type.register 'application/json', :json, %w(text/x-json application/jsonrequest application/jrd+json application/activity+json application/ld+json)
 Mime::Type.register 'text/xml',         :xml,  %w(application/xml application/atom+xml application/xrd+xml)
diff --git a/spec/controllers/accounts_controller_spec.rb b/spec/controllers/accounts_controller_spec.rb
index d61c8c9bd35c2b3752cc14d206a667dd7a4b6ba3..2c0df0ef3b517b9a18e75296a0c70ad95d363b12 100644
--- a/spec/controllers/accounts_controller_spec.rb
+++ b/spec/controllers/accounts_controller_spec.rb
@@ -48,6 +48,10 @@ RSpec.describe AccountsController, type: :controller do
       it 'returns http success with Activity Streams 2.0' do
         expect(response).to have_http_status(:success)
       end
+
+      it 'returns application/activity+json' do
+        expect(response.content_type).to eq 'application/activity+json'
+      end
     end
 
     context 'html' do
diff --git a/spec/controllers/activitypub/outboxes_controller_spec.rb b/spec/controllers/activitypub/outboxes_controller_spec.rb
index f98e4a8c38c536068abe861fda2744cdfabb3e4e..a2599802169e417983c407b25f54044ee60ccac5 100644
--- a/spec/controllers/activitypub/outboxes_controller_spec.rb
+++ b/spec/controllers/activitypub/outboxes_controller_spec.rb
@@ -15,5 +15,9 @@ RSpec.describe ActivityPub::OutboxesController, type: :controller do
     it 'returns http success' do
       expect(response).to have_http_status(:success)
     end
+
+    it 'returns application/activity+json' do
+      expect(response.content_type).to eq 'application/activity+json'
+    end
   end
 end