diff --git a/rack-attack.gemspec b/rack-attack.gemspec
index f2e6d9c..ca39cf0 100644
--- a/rack-attack.gemspec
+++ b/rack-attack.gemspec
@@ -32,6 +32,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'rack'
 
   s.add_development_dependency 'appraisal', '~> 2.2'
+  s.add_development_dependency "bundler", "~> 1.16"
   s.add_development_dependency 'minitest', "~> 5.11"
   s.add_development_dependency "minitest-stub-const", "~> 0.6"
   s.add_development_dependency 'rack-test', "~> 1.0"