diff --git a/Gemfile b/Gemfile
index 020badaa..2e5fefb6 100644
--- a/Gemfile
+++ b/Gemfile
@@ -3,12 +3,23 @@ source "https://rubygems.org"
 gemspec
 
 group :development do
+  gem 'committee', '2.0.0.pre6'
   gem 'mocha', '~> 0.13.2'
   gem 'rake'
   gem 'shoulda-context'
+  gem 'sinatra'
   gem 'test-unit'
   gem 'webmock'
 
+  # Rack 2.0+ requires Ruby >= 2.2.2 which is problematic for the test suite on
+  # older Ruby versions. Check Ruby the version here and put a maximum
+  # constraint on Rack if necessary.
+  if RUBY_VERSION >= '2.2.2'
+    gem "rack", ">= 1.5"
+  else
+    gem "rack", ">= 1.5", "< 2.0"
+  end
+
   platforms :mri do
     # to avoid problems, bring Byebug in on just versions of Ruby under which
     # it's known to work well