diff --git a/rubocop-thread_safety.gemspec b/rubocop-thread_safety.gemspec
index 6050be9..94f3aa6 100644
--- a/rubocop-thread_safety.gemspec
+++ b/rubocop-thread_safety.gemspec
@@ -38,6 +38,7 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency 'appraisal'
   spec.add_development_dependency 'bundler', '>= 1.10', '< 3'
+  spec.add_development_dependency 'prism'
   spec.add_development_dependency 'pry' unless ENV['CI']
   spec.add_development_dependency 'rake', '>= 10.0'
   spec.add_development_dependency 'rspec', '~> 3.0'