--- a/unf_ext.gemspec
+++ b/unf_ext.gemspec
@@ -12,7 +12,7 @@
   gem.homepage      = "https://github.com/knu/ruby-unf_ext"
   gem.licenses      = ["MIT"]
 
-  gem.files         = `git ls-files`.split($/)
+  gem.files         = Dir["ext/**/*", "lib/**/*.rb"]
   gem.executables   = gem.files.grep(%r{^bin/}).map{ |f| File.basename(f) }
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/}).grep(%r{/test_[^/]+\.rb$})
   gem.require_paths = ["lib"]