diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3713c9523..a6b729a9f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,13 @@
 Changelog
 =========
 
+## TBD
+
+### Enhancements
+
+* Sidekiq now uses `thread_queue` delivery by default
+  | [#626](https://github.com/bugsnag/bugsnag-ruby/pull/626)
+
 ## 6.16.0 (12 August 2020)
 
 ### Enhancements
diff --git a/features/fixtures/docker-compose.yml b/features/fixtures/docker-compose.yml
index 0357d5fb5..b5815d43e 100644
--- a/features/fixtures/docker-compose.yml
+++ b/features/fixtures/docker-compose.yml
@@ -262,6 +262,7 @@ services:
       - BUGSNAG_APP_VERSION
       - BUGSNAG_AUTO_CAPTURE_SESSIONS
       - BUGSNAG_AUTO_NOTIFY
+      - BUGSNAG_DELIVERY_METHOD
       - BUGSNAG_ENDPOINT
       - BUGSNAG_IGNORE_CLASS
       - BUGSNAG_IGNORE_MESSAGE
diff --git a/features/fixtures/sidekiq/app/app.rb b/features/fixtures/sidekiq/app/app.rb
index 44e9b50fe..436325940 100644
--- a/features/fixtures/sidekiq/app/app.rb
+++ b/features/fixtures/sidekiq/app/app.rb
@@ -6,6 +6,17 @@
   conf.api_key = ENV['BUGSNAG_API_KEY']
   puts "Configuring `endpoint` to #{ENV['BUGSNAG_ENDPOINT']}"
   conf.endpoint = ENV['BUGSNAG_ENDPOINT']
+
+  if ENV.include?('BUGSNAG_DELIVERY_METHOD')
+    puts "Configuring `delivery_method` to #{ENV['BUGSNAG_DELIVERY_METHOD']}"
+    conf.delivery_method = ENV['BUGSNAG_DELIVERY_METHOD'].to_sym
+  end
+
+  conf.add_on_error(proc do |report|
+    report.add_tab(:config, {
+      delivery_method: conf.delivery_method.to_s
+    })
+  end)
 end
 
 Sidekiq.configure_client do |config|
@@ -32,4 +43,4 @@ class UnhandledError
   def perform
     raise RuntimeError.new("Unhandled")
   end
-end
\ No newline at end of file
+end
diff --git a/features/sidekiq.feature b/features/sidekiq.feature
index a7842fa0c..499520170 100644
--- a/features/sidekiq.feature
+++ b/features/sidekiq.feature
@@ -11,10 +11,11 @@ Scenario: An unhandled RuntimeError sends a report
   And the event "severityReason.attributes.framework" equals "Sidekiq"
   And the exception "errorClass" equals "RuntimeError"
   And the "file" of stack frame 0 equals "/app/app.rb"
-  And the "lineNumber" of stack frame 0 equals 33
+  And the "lineNumber" of stack frame 0 equals 44
   And the payload field "events.0.metaData.sidekiq" matches the appropriate Sidekiq unhandled payload
   And the event "metaData.sidekiq.msg.created_at" is a parsable timestamp in seconds
   And the event "metaData.sidekiq.msg.enqueued_at" is a parsable timestamp in seconds
+  And the event "metaData.config.delivery_method" equals "thread_queue"
 
 Scenario: A handled RuntimeError can be notified
   Given I run the service "sidekiq" with the command "bundle exec rake sidekiq_tests:handled_error"
@@ -27,4 +28,20 @@ Scenario: A handled RuntimeError can be notified
   And the exception "errorClass" equals "RuntimeError"
   And the payload field "events.0.metaData.sidekiq" matches the appropriate Sidekiq handled payload
   And the event "metaData.sidekiq.msg.created_at" is a parsable timestamp in seconds
-  And the event "metaData.sidekiq.msg.enqueued_at" is a parsable timestamp in seconds
\ No newline at end of file
+  And the event "metaData.sidekiq.msg.enqueued_at" is a parsable timestamp in seconds
+  And the event "metaData.config.delivery_method" equals "thread_queue"
+
+Scenario: Synchronous delivery can be used
+  Given I set environment variable "BUGSNAG_DELIVERY_METHOD" to "synchronous"
+  And I run the service "sidekiq" with the command "bundle exec rake sidekiq_tests:handled_error"
+  And I wait to receive a request
+  Then the request is valid for the error reporting API version "4.0" for the "Ruby Bugsnag Notifier"
+  And the event "unhandled" is false
+  And the event "context" equals "HandledError@default"
+  And the event "severity" equals "warning"
+  And the event "severityReason.type" equals "handledException"
+  And the exception "errorClass" equals "RuntimeError"
+  And the payload field "events.0.metaData.sidekiq" matches the appropriate Sidekiq handled payload
+  And the event "metaData.sidekiq.msg.created_at" is a parsable timestamp in seconds
+  And the event "metaData.sidekiq.msg.enqueued_at" is a parsable timestamp in seconds
+  And the event "metaData.config.delivery_method" equals "synchronous"
diff --git a/lib/bugsnag/integrations/sidekiq.rb b/lib/bugsnag/integrations/sidekiq.rb
index b2590e5b1..3fcb4c2bc 100644
--- a/lib/bugsnag/integrations/sidekiq.rb
+++ b/lib/bugsnag/integrations/sidekiq.rb
@@ -14,7 +14,6 @@ class Sidekiq
     def initialize
       Bugsnag.configuration.internal_middleware.use(Bugsnag::Middleware::Sidekiq)
       Bugsnag.configuration.detected_app_type = "sidekiq"
-      Bugsnag.configuration.default_delivery_method = :synchronous
       Bugsnag.configuration.runtime_versions["sidekiq"] = ::Sidekiq::VERSION
     end