diff --git a/middleman.gemspec b/middleman.gemspec
index ef0de7b2..1188fe82 100644
--- a/middleman.gemspec
+++ b/middleman.gemspec
@@ -28,6 +28,8 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency("padrino-core", ["~> 0.9.23"])
   s.add_runtime_dependency("padrino-helpers", ["~> 0.9.23"])
   s.add_runtime_dependency("rack-test", ["~> 0.5.0"])
+  s.add_runtime_dependency("therubyracer", ["~> 0.8.0"]) unless defined?(JRUBY_VERSION)
+  s.add_runtime_dependency("therubyrhino", ["~> 1.72.0"]) if defined?(JRUBY_VERSION)
   s.add_runtime_dependency("uglifier", ["~> 0.5.0"])
   s.add_runtime_dependency("haml", ["~> 3.1.0"])
   s.add_runtime_dependency("sass", ["~> 3.1.0"])