diff --git a/.gitignore b/.gitignore
index 3df710d..0ade9b1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,3 +8,4 @@ spec/*.lock
 doc
 .yardoc
 Gemfile.lock
+gemfiles/Gemfile.2_4_0.lock
diff --git a/.travis.yml b/.travis.yml
index b3c7858..fcde422 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,6 +17,8 @@ matrix:
       gemfile: gemfiles/Gemfile.with_rack16
     - rvm: 2.3.1
       gemfile: gemfiles/Gemfile.with_rack2
+    - rvm: 2.4.0-preview2
+      gemfile: gemfiles/Gemfile.2_4_0
 
 notifications:
   email:
diff --git a/Gemfile b/Gemfile
index 37ee7f6..c4d4b6b 100644
--- a/Gemfile
+++ b/Gemfile
@@ -14,6 +14,10 @@ group :test do
   gem "coveralls", "~>0.8", require: false
   gem "simplecov", "~>0.10", require: false
   gem "codeclimate-test-reporter", "~>0.4"
-  gem "json"
+  if RUBY_VERSION > "2"
+    gem "json", "~> 2.0", ">= 2.0.2"
+  else
+    gem "json"
+  end
   gem "rspec", "< 4"
 end
diff --git a/gemfiles/Gemfile.2_4_0 b/gemfiles/Gemfile.2_4_0
new file mode 100644
index 0000000..f48ce89
--- /dev/null
+++ b/gemfiles/Gemfile.2_4_0
@@ -0,0 +1,3 @@
+eval_gemfile File.expand_path('../../Gemfile', __FILE__)
+gem 'rack', '>= 2'
+