diff --git a/gemfiles/activemodel-5 b/gemfiles/activemodel-5
index ac6588b..0c4ba36 100644
--- a/gemfiles/activemodel-5
+++ b/gemfiles/activemodel-5
@@ -1,5 +1,7 @@
 source 'https://rubygems.org'
 
+gem 'concurrent-ruby', '< 1.3.5' # https://github.com/rails/rails/pull/54264
+
 gem 'activemodel', '~> 5.0'
 gem 'rake'
 gem 'rspec', '~> 3.0'
diff --git a/gemfiles/activemodel-6 b/gemfiles/activemodel-6
index c58ab2d..1feec7b 100644
--- a/gemfiles/activemodel-6
+++ b/gemfiles/activemodel-6
@@ -1,5 +1,7 @@
 source 'https://rubygems.org'
 
+gem 'concurrent-ruby', '< 1.3.5' # https://github.com/rails/rails/pull/54264
+
 gem 'activemodel', '~> 6.0'
 gem 'rake'
 gem 'rspec', '~> 3.0'
diff --git a/gemfiles/activemodel-7 b/gemfiles/activemodel-7
index 1d0c23f..a3b6b9c 100644
--- a/gemfiles/activemodel-7
+++ b/gemfiles/activemodel-7
@@ -1,5 +1,7 @@
 source 'https://rubygems.org'
 
+gem 'concurrent-ruby', '< 1.3.5' # https://github.com/rails/rails/pull/54264
+
 gem 'activemodel', '~> 7.0'
 gem 'rake'
 gem 'rspec', '~> 3.0'
diff --git a/gemfiles/activemodel-8 b/gemfiles/activemodel-8
index 9b26a78..a7e0297 100644
--- a/gemfiles/activemodel-8
+++ b/gemfiles/activemodel-8
@@ -1,5 +1,7 @@
 source 'https://rubygems.org'
 
+gem 'concurrent-ruby', '< 1.3.5' # https://github.com/rails/rails/pull/54264
+
 gem 'activemodel', '~> 8.0'
 gem 'rake'
 gem 'rspec', '~> 3.13'