diff --git a/spring.gemspec b/spring.gemspec
index 99834785..9fa76bb9 100644
--- a/spring.gemspec
+++ b/spring.gemspec
@@ -15,6 +15,8 @@ Gem::Specification.new do |gem|
 
   gem.required_ruby_version = ">= 2.7.0"
 
+  gem.add_dependency 'mutex_m'
+
   gem.add_development_dependency 'rake'
   gem.add_development_dependency 'bump'
   gem.add_development_dependency 'activesupport'