diff --git a/gemfiles/gemfile_60.gemfile b/gemfiles/gemfile_60.gemfile
index b2e1109..3aaa49d 100644
--- a/gemfiles/gemfile_60.gemfile
+++ b/gemfiles/gemfile_60.gemfile
@@ -7,5 +7,6 @@ gem "activerecord", "~> 6.0.6"
 gem "mysql2"
 gem "pg"
 gem "sqlite3", "~> 1.6.9"
+gem "concurrent-ruby", "< 1.3.5"
 
 gemspec path: "../"
diff --git a/gemfiles/gemfile_61.gemfile b/gemfiles/gemfile_61.gemfile
index 539c700..a4fa370 100644
--- a/gemfiles/gemfile_61.gemfile
+++ b/gemfiles/gemfile_61.gemfile
@@ -7,5 +7,6 @@ gem "activerecord", "~> 6.1.7"
 gem "mysql2"
 gem "pg"
 gem "sqlite3", "~> 1.6.9"
+gem "concurrent-ruby", "< 1.3.5"
 
 gemspec path: "../"
diff --git a/gemfiles/gemfile_70.gemfile b/gemfiles/gemfile_70.gemfile
index 8979688..6573b79 100644
--- a/gemfiles/gemfile_70.gemfile
+++ b/gemfiles/gemfile_70.gemfile
@@ -7,5 +7,6 @@ gem "activerecord", "~> 7.0.8"
 gem "mysql2"
 gem "pg"
 gem "sqlite3", "< 2.0"
+gem "concurrent-ruby", "< 1.3.5"
 
 gemspec path: "../"
diff --git a/gemfiles/gemfile_71.gemfile b/gemfiles/gemfile_71.gemfile
index 32caf09..7c154ac 100644
--- a/gemfiles/gemfile_71.gemfile
+++ b/gemfiles/gemfile_71.gemfile
@@ -7,5 +7,6 @@ gem "activerecord", "~> 7.1.3"
 gem "mysql2"
 gem "pg"
 gem "sqlite3", "< 2.0"
+gem "concurrent-ruby", "< 1.3.5"
 
 gemspec path: "../"