diff --git a/execjs.gemspec b/execjs.gemspec
index 4b29f7a..ec49b49 100644
--- a/execjs.gemspec
+++ b/execjs.gemspec
@@ -12,6 +12,7 @@ Gem::Specification.new do |s|
   s.files = [
     "lib/execjs.rb",
     "lib/execjs/external_runtime.rb",
+    "lib/execjs/module.rb",
     "lib/execjs/mustang_runtime.rb",
     "lib/execjs/ruby_racer_runtime.rb",
     "lib/execjs/ruby_rhino_runtime.rb",