diff --git a/rails.gemspec b/rails.gemspec
index b426faf0e8..d1c199a97a 100644
--- a/rails.gemspec
+++ b/rails.gemspec
@@ -21,6 +21,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'activesupport', version
   s.add_dependency 'actionpack',    version
   s.add_dependency 'actionview',    version
+  s.add_dependency 'activemodel',   version
   s.add_dependency 'activerecord',  version
   s.add_dependency 'actionmailer',  version
   s.add_dependency 'railties',      version