diff --git a/sidekiq.gemspec b/sidekiq.gemspec
index b60907e45..06b19fed0 100644
--- a/sidekiq.gemspec
+++ b/sidekiq.gemspec
@@ -16,6 +16,6 @@ Gem::Specification.new do |gem|
 
   gem.add_dependency 'redis', '>= 3.3.5', '< 5'
   gem.add_dependency 'connection_pool', '~> 2.2', '>= 2.2.2'
-  gem.add_dependency 'rack', '>= 1.5.0'
+  gem.add_dependency 'rack', '< 2.1.0'
   gem.add_dependency 'rack-protection', '>= 1.5.0'
 end