diff --git a/.gitignore b/.gitignore
index 5d1746d..4144a99 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ Gemfile.lock
 *.swp
 *.gem
 pkg
++/gemfiles/*.lock
diff --git a/Appraisals b/Appraisals
new file mode 100644
index 0000000..a93e00a
--- /dev/null
+++ b/Appraisals
@@ -0,0 +1,20 @@
+# Install gems for all appraisal definitions:
+#
+#     $ appraisal install
+#
+# To run tests on different versions:
+#
+#     $ appraisal activesupport_x.x rspec spec
+
+[
+  [ '3.2', '~> 3.2.0' ],
+  [ '4.0', '~> 4.0.0' ],
+  [ '4.1', '~> 4.1.0' ],
+  [ '4.2', '~> 4.2.0' ],
+].each do |ver_name, ver_req|
+  # Note: for the rake task to work, these definition names must be the same as the corresponding
+  # filename produced in "gemfiles/", i.e. all characters must be in this set: [A-Za-z0-9_.]
+  appraise "activesupport_#{ver_name}" do
+    gem 'activesupport', ver_req
+  end
+end
diff --git a/add_http_header.gemspec b/add_http_header.gemspec
index 5a4e845..d6848fc 100644
--- a/add_http_header.gemspec
+++ b/add_http_header.gemspec
@@ -18,7 +18,8 @@ Gem::Specification.new do |spec|
 
   spec.add_runtime_dependency 'activesupport', '>= 0'
 
-  spec.add_development_dependency 'rspec', '~> 2.8.0'
+  spec.add_development_dependency 'rspec', '~> 2.99'
   spec.add_development_dependency 'bundler', '~> 1.7'
   spec.add_development_dependency 'rake', '~> 10.0'
+  spec.add_development_dependency 'appraisal'
 end
diff --git a/gemfiles/activesupport_3.2.gemfile b/gemfiles/activesupport_3.2.gemfile
new file mode 100644
index 0000000..61efc24
--- /dev/null
+++ b/gemfiles/activesupport_3.2.gemfile
@@ -0,0 +1,7 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "activesupport", "~> 3.2.0"
+
+gemspec :path => "../"
diff --git a/gemfiles/activesupport_4.0.gemfile b/gemfiles/activesupport_4.0.gemfile
new file mode 100644
index 0000000..697ad67
--- /dev/null
+++ b/gemfiles/activesupport_4.0.gemfile
@@ -0,0 +1,7 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "activesupport", "~> 4.0.0"
+
+gemspec :path => "../"
diff --git a/gemfiles/activesupport_4.1.gemfile b/gemfiles/activesupport_4.1.gemfile
new file mode 100644
index 0000000..670c4f8
--- /dev/null
+++ b/gemfiles/activesupport_4.1.gemfile
@@ -0,0 +1,7 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "activesupport", "~> 4.1.0"
+
+gemspec :path => "../"
diff --git a/gemfiles/activesupport_4.2.gemfile b/gemfiles/activesupport_4.2.gemfile
new file mode 100644
index 0000000..5bfd361
--- /dev/null
+++ b/gemfiles/activesupport_4.2.gemfile
@@ -0,0 +1,7 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "activesupport", "~> 4.2.0"
+
+gemspec :path => "../"