diff --git a/CHANGELOG.md b/CHANGELOG.md
index 14749caa3..2a932250b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,17 @@
 
 All notable changes to this project will be documented in this file.
 
+## [4.2.7] - 2024-02-16
+
+### Fixed
+
+- Fix OmniAuth tests and edge cases in error handling ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29201), [ClearlyClaire](https://github.com/mastodon/mastodon/pull/29207))
+- Fix new installs by upgrading to the latest release of the `nsa` gem, instead of a no longer existing commit ([mjankowski](https://github.com/mastodon/mastodon/pull/29065))
+
+### Security
+
+- Fix insufficient checking of remote posts ([GHSA-jhrq-qvrm-qr36](https://github.com/mastodon/mastodon/security/advisories/GHSA-jhrq-qvrm-qr36))
+
 ## [4.2.6] - 2024-02-14
 
 ### Security
diff --git a/Gemfile b/Gemfile
index 6f20ff25a..829e7d857 100644
--- a/Gemfile
+++ b/Gemfile
@@ -61,7 +61,7 @@ gem 'kaminari', '~> 1.2'
 gem 'link_header', '~> 0.0'
 gem 'mime-types', '~> 3.5.0', require: 'mime/types/columnar'
 gem 'nokogiri', '~> 1.15'
-gem 'nsa', github: 'jhawthorn/nsa', ref: 'e020fcc3a54d993ab45b7194d89ab720296c111b'
+gem 'nsa'
 gem 'oj', '~> 3.14'
 gem 'ox', '~> 2.14'
 gem 'parslet'
diff --git a/Gemfile.lock b/Gemfile.lock
index 1c767859b..134e41a7e 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -7,17 +7,6 @@ GIT
       hkdf (~> 0.2)
       jwt (~> 2.0)
 
-GIT
-  remote: https://github.com/jhawthorn/nsa.git
-  revision: e020fcc3a54d993ab45b7194d89ab720296c111b
-  ref: e020fcc3a54d993ab45b7194d89ab720296c111b
-  specs:
-    nsa (0.2.8)
-      activesupport (>= 4.2, < 7.2)
-      concurrent-ruby (~> 1.0, >= 1.0.2)
-      sidekiq (>= 3.5)
-      statsd-ruby (~> 1.4, >= 1.4.0)
-
 GIT
   remote: https://github.com/mastodon/rails-settings-cached.git
   revision: 86328ef0bd04ce21cc0504ff5e334591e8c2ccab
@@ -483,6 +472,11 @@ GEM
     nokogiri (1.16.2)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
+    nsa (0.3.0)
+      activesupport (>= 4.2, < 7.2)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      sidekiq (>= 3.5)
+      statsd-ruby (~> 1.4, >= 1.4.0)
     oj (3.16.1)
     omniauth (2.1.1)
       hashie (>= 3.4.6)
@@ -520,7 +514,7 @@ GEM
     parslet (2.0.0)
     pastel (0.8.0)
       tty-color (~> 0.5)
-    pg (1.5.4)
+    pg (1.5.5)
     pghero (3.3.4)
       activerecord (>= 6)
     posix-spawn (0.3.15)
@@ -884,7 +878,7 @@ DEPENDENCIES
   net-http (~> 0.3.2)
   net-ldap (~> 0.18)
   nokogiri (~> 1.15)
-  nsa!
+  nsa
   oj (~> 3.14)
   omniauth (~> 2.0)
   omniauth-cas!
diff --git a/app/controllers/auth/omniauth_callbacks_controller.rb b/app/controllers/auth/omniauth_callbacks_controller.rb
index 7bccac7f6..b8570d0bf 100644
--- a/app/controllers/auth/omniauth_callbacks_controller.rb
+++ b/app/controllers/auth/omniauth_callbacks_controller.rb
@@ -16,6 +16,9 @@ class Auth::OmniauthCallbacksController < Devise::OmniauthCallbacksController
         session["devise.#{provider}_data"] = request.env['omniauth.auth']
         redirect_to new_user_registration_url
       end
+    rescue ActiveRecord::RecordInvalid
+      flash[:alert] = I18n.t('devise.failure.omniauth_user_creation_failure') if is_navigational_format?
+      redirect_to new_user_session_url
     end
   end
 
diff --git a/app/helpers/jsonld_helper.rb b/app/helpers/jsonld_helper.rb
index cc05b7a40..b0f2077db 100644
--- a/app/helpers/jsonld_helper.rb
+++ b/app/helpers/jsonld_helper.rb
@@ -174,7 +174,19 @@ module JsonLdHelper
     build_request(uri, on_behalf_of, options: request_options).perform do |response|
       raise Mastodon::UnexpectedResponseError, response unless response_successful?(response) || response_error_unsalvageable?(response) || !raise_on_temporary_error
 
-      body_to_json(response.body_with_limit) if response.code == 200
+      body_to_json(response.body_with_limit) if response.code == 200 && valid_activitypub_content_type?(response)
+    end
+  end
+
+  def valid_activitypub_content_type?(response)
+    return true if response.mime_type == 'application/activity+json'
+
+    # When the mime type is `application/ld+json`, we need to check the profile,
+    # but `http.rb` does not parse it for us.
+    return false unless response.mime_type == 'application/ld+json'
+
+    response.headers[HTTP::Headers::CONTENT_TYPE]&.split(';')&.map(&:strip)&.any? do |str|
+      str.start_with?('profile="') && str[9...-1].split.include?('https://www.w3.org/ns/activitystreams')
     end
   end
 
diff --git a/app/services/fetch_resource_service.rb b/app/services/fetch_resource_service.rb
index 71c6cca79..84c36f6a1 100644
--- a/app/services/fetch_resource_service.rb
+++ b/app/services/fetch_resource_service.rb
@@ -44,7 +44,7 @@ class FetchResourceService < BaseService
     @response_code = response.code
     return nil if response.code != 200
 
-    if ['application/activity+json', 'application/ld+json'].include?(response.mime_type)
+    if valid_activitypub_content_type?(response)
       body = response.body_with_limit
       json = body_to_json(body)
 
diff --git a/config/locales/devise.en-DG.yml b/config/locales/devise.en-DG.yml
index 93d0ecc4d..654e8584e 100644
--- a/config/locales/devise.en-DG.yml
+++ b/config/locales/devise.en-DG.yml
@@ -12,6 +12,7 @@ en-DG:
       last_attempt: You have one more attempt before your account is locked.
       locked: Your account is locked.
       not_found_in_database: Invalid %{authentication_keys} or password.
+      omniauth_user_creation_failure: Error creating an account for this identity.
       pending: Your account is still under review.
       timeout: Your session expired. Please login again to continue.
       unauthenticated: You need to login or sign up before continuing.
diff --git a/config/locales/devise.en-LN.yml b/config/locales/devise.en-LN.yml
index 65ccffce8..ba61b77dd 100644
--- a/config/locales/devise.en-LN.yml
+++ b/config/locales/devise.en-LN.yml
@@ -12,6 +12,7 @@ en-LN:
       last_attempt: You have one more attempt before your account is locked.
       locked: Your account is locked.
       not_found_in_database: Invalid %{authentication_keys} or password.
+      omniauth_user_creation_failure: Error creating an account for this identity.
       pending: Your account is still under review.
       timeout: Your session expired. Please login again to continue.
       unauthenticated: You need to login or sign up before continuing.
diff --git a/config/locales/devise.en-SQ.yml b/config/locales/devise.en-SQ.yml
index d59947035..62009b4b0 100644
--- a/config/locales/devise.en-SQ.yml
+++ b/config/locales/devise.en-SQ.yml
@@ -12,6 +12,7 @@ en-SQ:
       last_attempt: You have one more attempt before your account is locked.
       locked: Your account is locked.
       not_found_in_database: Invalid %{authentication_keys} or password.
+      omniauth_user_creation_failure: Error creating an account for this identity.
       pending: Your account is still under review.
       timeout: Your session expired. Please login again to continue.
       unauthenticated: You need to login or sign up before continuing.
diff --git a/config/locales/devise.en.yml b/config/locales/devise.en.yml
index eef821481..b7c060016 100644
--- a/config/locales/devise.en.yml
+++ b/config/locales/devise.en.yml
@@ -12,6 +12,7 @@ en:
       last_attempt: You have one more attempt before your account is locked.
       locked: Your account is locked.
       not_found_in_database: Invalid %{authentication_keys} or password.
+      omniauth_user_creation_failure: Error creating an account for this identity.
       pending: Your account is still under review.
       timeout: Your session expired. Please login again to continue.
       unauthenticated: You need to login or sign up before continuing.
diff --git a/docker-compose.yml b/docker-compose.yml
index 2f03db04d..4563e2317 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -56,7 +56,7 @@ services:
 
   web:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.6
+    image: ghcr.io/mastodon/mastodon:v4.2.7
     restart: always
     env_file: .env.production
     command: bash -c "rm -f /mastodon/tmp/pids/server.pid; bundle exec rails s -p 3000"
@@ -77,7 +77,7 @@ services:
 
   streaming:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.6
+    image: ghcr.io/mastodon/mastodon:v4.2.7
     restart: always
     env_file: .env.production
     command: node ./streaming
@@ -95,7 +95,7 @@ services:
 
   sidekiq:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.6
+    image: ghcr.io/mastodon/mastodon:v4.2.7
     restart: always
     env_file: .env.production
     command: bundle exec sidekiq
diff --git a/lib/mastodon/version.rb b/lib/mastodon/version.rb
index 07aeadeb3..9788a70cb 100644
--- a/lib/mastodon/version.rb
+++ b/lib/mastodon/version.rb
@@ -13,7 +13,7 @@ module Mastodon
     end
 
     def patch
-      6
+      7
     end
 
     def default_prerelease
diff --git a/spec/helpers/jsonld_helper_spec.rb b/spec/helpers/jsonld_helper_spec.rb
index 3575bba85..6367492b9 100644
--- a/spec/helpers/jsonld_helper_spec.rb
+++ b/spec/helpers/jsonld_helper_spec.rb
@@ -56,15 +56,15 @@ describe JsonLdHelper do
   describe '#fetch_resource' do
     context 'when the second argument is false' do
       it 'returns resource even if the retrieved ID and the given URI does not match' do
-        stub_request(:get, 'https://bob.test/').to_return body: '{"id": "https://alice.test/"}'
-        stub_request(:get, 'https://alice.test/').to_return body: '{"id": "https://alice.test/"}'
+        stub_request(:get, 'https://bob.test/').to_return(body: '{"id": "https://alice.test/"}', headers: { 'Content-Type': 'application/activity+json' })
+        stub_request(:get, 'https://alice.test/').to_return(body: '{"id": "https://alice.test/"}', headers: { 'Content-Type': 'application/activity+json' })
 
         expect(fetch_resource('https://bob.test/', false)).to eq({ 'id' => 'https://alice.test/' })
       end
 
       it 'returns nil if the object identified by the given URI and the object identified by the retrieved ID does not match' do
-        stub_request(:get, 'https://mallory.test/').to_return body: '{"id": "https://marvin.test/"}'
-        stub_request(:get, 'https://marvin.test/').to_return body: '{"id": "https://alice.test/"}'
+        stub_request(:get, 'https://mallory.test/').to_return(body: '{"id": "https://marvin.test/"}', headers: { 'Content-Type': 'application/activity+json' })
+        stub_request(:get, 'https://marvin.test/').to_return(body: '{"id": "https://alice.test/"}', headers: { 'Content-Type': 'application/activity+json' })
 
         expect(fetch_resource('https://mallory.test/', false)).to be_nil
       end
@@ -72,7 +72,7 @@ describe JsonLdHelper do
 
     context 'when the second argument is true' do
       it 'returns nil if the retrieved ID and the given URI does not match' do
-        stub_request(:get, 'https://mallory.test/').to_return body: '{"id": "https://alice.test/"}'
+        stub_request(:get, 'https://mallory.test/').to_return(body: '{"id": "https://alice.test/"}', headers: { 'Content-Type': 'application/activity+json' })
         expect(fetch_resource('https://mallory.test/', true)).to be_nil
       end
     end
@@ -80,12 +80,12 @@ describe JsonLdHelper do
 
   describe '#fetch_resource_without_id_validation' do
     it 'returns nil if the status code is not 200' do
-      stub_request(:get, 'https://host.test/').to_return status: 400, body: '{}'
+      stub_request(:get, 'https://host.test/').to_return(status: 400, body: '{}', headers: { 'Content-Type': 'application/activity+json' })
       expect(fetch_resource_without_id_validation('https://host.test/')).to be_nil
     end
 
     it 'returns hash' do
-      stub_request(:get, 'https://host.test/').to_return status: 200, body: '{}'
+      stub_request(:get, 'https://host.test/').to_return(status: 200, body: '{}', headers: { 'Content-Type': 'application/activity+json' })
       expect(fetch_resource_without_id_validation('https://host.test/')).to eq({})
     end
   end
diff --git a/spec/lib/activitypub/activity/announce_spec.rb b/spec/lib/activitypub/activity/announce_spec.rb
index 8ad892975..b556bfd6c 100644
--- a/spec/lib/activitypub/activity/announce_spec.rb
+++ b/spec/lib/activitypub/activity/announce_spec.rb
@@ -35,7 +35,7 @@ RSpec.describe ActivityPub::Activity::Announce do
     context 'when sender is followed by a local account' do
       before do
         Fabricate(:account).follow!(sender)
-        stub_request(:get, 'https://example.com/actor/hello-world').to_return(body: Oj.dump(unknown_object_json))
+        stub_request(:get, 'https://example.com/actor/hello-world').to_return(body: Oj.dump(unknown_object_json), headers: { 'Content-Type': 'application/activity+json' })
         subject.perform
       end
 
@@ -120,7 +120,7 @@ RSpec.describe ActivityPub::Activity::Announce do
       let(:object_json) { 'https://example.com/actor/hello-world' }
 
       before do
-        stub_request(:get, 'https://example.com/actor/hello-world').to_return(body: Oj.dump(unknown_object_json))
+        stub_request(:get, 'https://example.com/actor/hello-world').to_return(body: Oj.dump(unknown_object_json), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       context 'when the relay is enabled' do
diff --git a/spec/requests/omniauth_callbacks_spec.rb b/spec/requests/omniauth_callbacks_spec.rb
index c40ef14c9..6381bf066 100644
--- a/spec/requests/omniauth_callbacks_spec.rb
+++ b/spec/requests/omniauth_callbacks_spec.rb
@@ -39,16 +39,35 @@ describe 'OmniAuth callbacks' do
           Fabricate(:user, email: 'user@host.example')
         end
 
-        it 'matches the existing user, creates an identity, and redirects to root path' do
-          expect { subject }
-            .to not_change(User, :count)
-            .and change(Identity, :count)
-            .by(1)
-            .and change(LoginActivity, :count)
-            .by(1)
+        context 'when ALLOW_UNSAFE_AUTH_PROVIDER_REATTACH is set to true' do
+          around do |example|
+            ClimateControl.modify ALLOW_UNSAFE_AUTH_PROVIDER_REATTACH: 'true' do
+              example.run
+            end
+          end
 
-          expect(Identity.find_by(user: User.last).uid).to eq('123')
-          expect(response).to redirect_to(root_path)
+          it 'matches the existing user, creates an identity, and redirects to root path' do
+            expect { subject }
+              .to not_change(User, :count)
+              .and change(Identity, :count)
+              .by(1)
+              .and change(LoginActivity, :count)
+              .by(1)
+
+            expect(Identity.find_by(user: User.last).uid).to eq('123')
+            expect(response).to redirect_to(root_path)
+          end
+        end
+
+        context 'when ALLOW_UNSAFE_AUTH_PROVIDER_REATTACH is not set to true' do
+          it 'does not match the existing user or create an identity, and redirects to login page' do
+            expect { subject }
+              .to not_change(User, :count)
+              .and not_change(Identity, :count)
+              .and not_change(LoginActivity, :count)
+
+            expect(response).to redirect_to(new_user_session_url)
+          end
         end
       end
 
diff --git a/spec/services/activitypub/fetch_featured_collection_service_spec.rb b/spec/services/activitypub/fetch_featured_collection_service_spec.rb
index a096296ff..583212c37 100644
--- a/spec/services/activitypub/fetch_featured_collection_service_spec.rb
+++ b/spec/services/activitypub/fetch_featured_collection_service_spec.rb
@@ -62,10 +62,10 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
 
   shared_examples 'sets pinned posts' do
     before do
-      stub_request(:get, 'https://example.com/account/pinned/known').to_return(status: 200, body: Oj.dump(status_json_pinned_known))
-      stub_request(:get, 'https://example.com/account/pinned/unknown-inlined').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_inlined))
+      stub_request(:get, 'https://example.com/account/pinned/known').to_return(status: 200, body: Oj.dump(status_json_pinned_known), headers: { 'Content-Type': 'application/activity+json' })
+      stub_request(:get, 'https://example.com/account/pinned/unknown-inlined').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_inlined), headers: { 'Content-Type': 'application/activity+json' })
       stub_request(:get, 'https://example.com/account/pinned/unknown-unreachable').to_return(status: 404)
-      stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable))
+      stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable), headers: { 'Content-Type': 'application/activity+json' })
 
       subject.call(actor, note: true, hashtag: false)
     end
@@ -82,7 +82,7 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
   describe '#call' do
     context 'when the endpoint is a Collection' do
       before do
-        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets pinned posts'
@@ -99,7 +99,7 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
       end
 
       before do
-        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets pinned posts'
@@ -108,7 +108,7 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
         let(:items) { 'https://example.com/account/pinned/unknown-reachable' }
 
         before do
-          stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable))
+          stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable), headers: { 'Content-Type': 'application/activity+json' })
           subject.call(actor, note: true, hashtag: false)
         end
 
@@ -135,7 +135,7 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
       end
 
       before do
-        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets pinned posts'
@@ -144,7 +144,7 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
         let(:items) { 'https://example.com/account/pinned/unknown-reachable' }
 
         before do
-          stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable))
+          stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable), headers: { 'Content-Type': 'application/activity+json' })
           subject.call(actor, note: true, hashtag: false)
         end
 
diff --git a/spec/services/activitypub/fetch_featured_tags_collection_service_spec.rb b/spec/services/activitypub/fetch_featured_tags_collection_service_spec.rb
index 071e4d92d..638278a10 100644
--- a/spec/services/activitypub/fetch_featured_tags_collection_service_spec.rb
+++ b/spec/services/activitypub/fetch_featured_tags_collection_service_spec.rb
@@ -38,7 +38,7 @@ RSpec.describe ActivityPub::FetchFeaturedTagsCollectionService, type: :service d
   describe '#call' do
     context 'when the endpoint is a Collection' do
       before do
-        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets featured tags'
@@ -46,7 +46,7 @@ RSpec.describe ActivityPub::FetchFeaturedTagsCollectionService, type: :service d
 
     context 'when the account already has featured tags' do
       before do
-        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
 
         actor.featured_tags.create!(name: 'FoO')
         actor.featured_tags.create!(name: 'baz')
@@ -67,7 +67,7 @@ RSpec.describe ActivityPub::FetchFeaturedTagsCollectionService, type: :service d
       end
 
       before do
-        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets featured tags'
@@ -88,7 +88,7 @@ RSpec.describe ActivityPub::FetchFeaturedTagsCollectionService, type: :service d
       end
 
       before do
-        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets featured tags'
diff --git a/spec/services/activitypub/fetch_remote_account_service_spec.rb b/spec/services/activitypub/fetch_remote_account_service_spec.rb
index f33a928da..42badde05 100644
--- a/spec/services/activitypub/fetch_remote_account_service_spec.rb
+++ b/spec/services/activitypub/fetch_remote_account_service_spec.rb
@@ -44,7 +44,7 @@ RSpec.describe ActivityPub::FetchRemoteAccountService, type: :service do
       before do
         actor[:inbox] = nil
 
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -67,7 +67,7 @@ RSpec.describe ActivityPub::FetchRemoteAccountService, type: :service do
       let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/alice' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -93,7 +93,7 @@ RSpec.describe ActivityPub::FetchRemoteAccountService, type: :service do
       let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/alice' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
         stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
@@ -125,7 +125,7 @@ RSpec.describe ActivityPub::FetchRemoteAccountService, type: :service do
       let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -148,7 +148,7 @@ RSpec.describe ActivityPub::FetchRemoteAccountService, type: :service do
       let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
         stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
diff --git a/spec/services/activitypub/fetch_remote_actor_service_spec.rb b/spec/services/activitypub/fetch_remote_actor_service_spec.rb
index 944a2f8b1..6d264b7b8 100644
--- a/spec/services/activitypub/fetch_remote_actor_service_spec.rb
+++ b/spec/services/activitypub/fetch_remote_actor_service_spec.rb
@@ -44,7 +44,7 @@ RSpec.describe ActivityPub::FetchRemoteActorService, type: :service do
       before do
         actor[:inbox] = nil
 
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -67,7 +67,7 @@ RSpec.describe ActivityPub::FetchRemoteActorService, type: :service do
       let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/alice' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -93,7 +93,7 @@ RSpec.describe ActivityPub::FetchRemoteActorService, type: :service do
       let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/alice' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
         stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
@@ -125,7 +125,7 @@ RSpec.describe ActivityPub::FetchRemoteActorService, type: :service do
       let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -148,7 +148,7 @@ RSpec.describe ActivityPub::FetchRemoteActorService, type: :service do
       let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
         stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
diff --git a/spec/services/activitypub/fetch_remote_key_service_spec.rb b/spec/services/activitypub/fetch_remote_key_service_spec.rb
index 0b14da4f4..478778cc9 100644
--- a/spec/services/activitypub/fetch_remote_key_service_spec.rb
+++ b/spec/services/activitypub/fetch_remote_key_service_spec.rb
@@ -50,7 +50,7 @@ RSpec.describe ActivityPub::FetchRemoteKeyService, type: :service do
   end
 
   before do
-    stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+    stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
     stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
   end
 
@@ -59,7 +59,7 @@ RSpec.describe ActivityPub::FetchRemoteKeyService, type: :service do
 
     context 'when the key is a sub-object from the actor' do
       before do
-        stub_request(:get, public_key_id).to_return(body: Oj.dump(actor))
+        stub_request(:get, public_key_id).to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it 'returns the expected account' do
@@ -71,7 +71,7 @@ RSpec.describe ActivityPub::FetchRemoteKeyService, type: :service do
       let(:public_key_id) { 'https://example.com/alice-public-key.json' }
 
       before do
-        stub_request(:get, public_key_id).to_return(body: Oj.dump(key_json.merge({ '@context': ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1'] })))
+        stub_request(:get, public_key_id).to_return(body: Oj.dump(key_json.merge({ '@context': ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1'] })), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it 'returns the expected account' do
@@ -84,7 +84,7 @@ RSpec.describe ActivityPub::FetchRemoteKeyService, type: :service do
       let(:actor_public_key) { 'https://example.com/alice-public-key.json' }
 
       before do
-        stub_request(:get, public_key_id).to_return(body: Oj.dump(key_json.merge({ '@context': ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1'] })))
+        stub_request(:get, public_key_id).to_return(body: Oj.dump(key_json.merge({ '@context': ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1'] })), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it 'returns the nil' do
diff --git a/spec/services/activitypub/fetch_replies_service_spec.rb b/spec/services/activitypub/fetch_replies_service_spec.rb
index 62841d7d2..73c2b4506 100644
--- a/spec/services/activitypub/fetch_replies_service_spec.rb
+++ b/spec/services/activitypub/fetch_replies_service_spec.rb
@@ -55,7 +55,7 @@ RSpec.describe ActivityPub::FetchRepliesService, type: :service do
 
       context 'when passing the URL to the collection' do
         before do
-          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
         end
 
         it 'spawns workers for up to 5 replies on the same server' do
@@ -84,7 +84,7 @@ RSpec.describe ActivityPub::FetchRepliesService, type: :service do
 
       context 'when passing the URL to the collection' do
         before do
-          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
         end
 
         it 'spawns workers for up to 5 replies on the same server' do
@@ -117,7 +117,7 @@ RSpec.describe ActivityPub::FetchRepliesService, type: :service do
 
       context 'when passing the URL to the collection' do
         before do
-          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
         end
 
         it 'spawns workers for up to 5 replies on the same server' do
diff --git a/spec/services/activitypub/synchronize_followers_service_spec.rb b/spec/services/activitypub/synchronize_followers_service_spec.rb
index c9a513e24..f62376ab9 100644
--- a/spec/services/activitypub/synchronize_followers_service_spec.rb
+++ b/spec/services/activitypub/synchronize_followers_service_spec.rb
@@ -60,7 +60,7 @@ RSpec.describe ActivityPub::SynchronizeFollowersService, type: :service do
   describe '#call' do
     context 'when the endpoint is a Collection of actor URIs' do
       before do
-        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'synchronizes followers'
@@ -77,7 +77,7 @@ RSpec.describe ActivityPub::SynchronizeFollowersService, type: :service do
       end
 
       before do
-        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'synchronizes followers'
@@ -98,7 +98,7 @@ RSpec.describe ActivityPub::SynchronizeFollowersService, type: :service do
       end
 
       before do
-        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'synchronizes followers'
diff --git a/spec/workers/activitypub/fetch_replies_worker_spec.rb b/spec/workers/activitypub/fetch_replies_worker_spec.rb
index ff4d049a2..2d080e286 100644
--- a/spec/workers/activitypub/fetch_replies_worker_spec.rb
+++ b/spec/workers/activitypub/fetch_replies_worker_spec.rb
@@ -21,7 +21,7 @@ describe ActivityPub::FetchRepliesWorker do
 
   describe 'perform' do
     it 'performs a request if the collection URI is from the same host' do
-      stub_request(:get, 'https://example.com/statuses_replies/1').to_return(status: 200, body: json)
+      stub_request(:get, 'https://example.com/statuses_replies/1').to_return(status: 200, body: json, headers: { 'Content-Type': 'application/activity+json' })
       subject.perform(status.id, 'https://example.com/statuses_replies/1')
       expect(a_request(:get, 'https://example.com/statuses_replies/1')).to have_been_made.once
     end