diff --git a/timecost.gemspec b/timecost.gemspec
index b244ab5..eba291e 100644
--- a/timecost.gemspec
+++ b/timecost.gemspec
@@ -18,6 +18,7 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ["lib"]
 
+  spec.add_runtime_dependency "activerecord", "~> 4.0"
   spec.add_development_dependency "bundler", "~> 1.6"
   spec.add_development_dependency "rake", "~> 10.0"
   spec.add_development_dependency "minitest", "~> 4.7.5"