diff --git a/.circleci/config.yml b/.circleci/config.yml
index 2c6609b6f..1cc182eee 100755
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -6,7 +6,7 @@ version: 2
 
 defaults: &defaults
   docker:
-    - image: circleci/ruby:2.5.1-node
+    - image: circleci/ruby:2.6.0-node
   working_directory: ~/api.goodcity
 
 jobs:
@@ -47,7 +47,7 @@ jobs:
   test:
     <<: *defaults
     docker:
-      - image: circleci/ruby:2.5.1-node
+      - image: circleci/ruby:2.6.0-node
       - image: circleci/postgres:9.6.9-alpine-ram
       - image: circleci/redis:4.0.9-alpine
     parallelism: 4
diff --git a/Gemfile b/Gemfile
index 2c67c6b3d..0ff9c43d1 100755
--- a/Gemfile
+++ b/Gemfile
@@ -1,5 +1,5 @@
 source 'https://rubygems.org'
-ruby "2.5.1"
+ruby "2.6.0"
 
 gem 'rails', '~> 4.2.11.1'
 gem 'rails-api'
diff --git a/Gemfile.lock b/Gemfile.lock
index a374db053..cc2cbee52 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -545,7 +545,7 @@ DEPENDENCIES
   with_advisory_lock
 
 RUBY VERSION
-   ruby 2.5.1p57
+   ruby 2.6.0p0
 
 BUNDLED WITH
    1.17.3
diff --git a/spec/support/controller_helpers.rb b/spec/support/controller_helpers.rb
index aac2d6216..f224032b2 100644
--- a/spec/support/controller_helpers.rb
+++ b/spec/support/controller_helpers.rb
@@ -1,6 +1,23 @@
 # test/test_helpers/warden.rb
-# Based on http://stackoverflow.com/questions/13420923/configuring-warden-for-use-in-rspec-controller-specs
 
+if RUBY_VERSION >= '2.6.0'
+  if Rails.version < '5'
+    module ActionController
+      class TestResponse < ActionDispatch::TestResponse
+        def recycle!
+          # HACK: to avoid MonitorMixin double-initialize error:
+          @mon_mutex_owner_object_id = nil
+          @mon_mutex = nil
+          initialize
+        end
+      end
+    end
+  else
+    puts 'Monkeypatch for ActionController::TestResponse no longer needed'
+  end
+end
+
+# Based on http://stackoverflow.com/questions/13420923/configuring-warden-for-use-in-rspec-controller-specs
 module Warden
   # Warden::Test::ControllerHelpers provides a facility to test controllers in isolation
   # Most of the code was extracted from Devise's Devise::TestHelpers.