diff --git a/elasticsearch-api/elasticsearch-api.gemspec b/elasticsearch-api/elasticsearch-api.gemspec
index a458ed60d..ebc59fcf0 100644
--- a/elasticsearch-api/elasticsearch-api.gemspec
+++ b/elasticsearch-api/elasticsearch-api.gemspec
@@ -49,7 +49,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'ansi'
   s.add_development_dependency 'bundler'
   s.add_development_dependency 'elasticsearch'
-  s.add_development_dependency 'elasticsearch-test-runner' unless defined?(JRUBY_VERSION) && JRUBY_VERSION <= "9.4"
+  s.add_development_dependency 'elasticsearch-test-runner' unless defined?(JRUBY_VERSION) && JRUBY_VERSION <= '9.4'
   s.add_development_dependency 'minitest'
   s.add_development_dependency 'minitest-reporters', '>= 1.6'
   s.add_development_dependency 'mocha'
@@ -59,6 +59,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'yard'
 
   # Gems for testing integrations
+  s.add_development_dependency 'concurrent-ruby', '1.3.4' if defined? JRUBY_VERSION && JRUBY_VERSION < '9.4'
   s.add_development_dependency 'jsonify'
   s.add_development_dependency 'hashie'
   # Temporary support for Ruby 2.6, since it's EOL March 2022: