diff --git a/logger.gemspec b/logger.gemspec
index d0b3e19..09d9600 100644
--- a/logger.gemspec
+++ b/logger.gemspec
@@ -15,7 +15,11 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://github.com/ruby/logger"
   spec.licenses      = ["Ruby", "BSD-2-Clause"]
 
-  spec.files         = Dir.glob("lib/**/*.rb") + ["logger.gemspec", "BSDL", "COPYING"]
+  # Specify which files should be added to the gem when it is released.
+  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
+  spec.files         = Dir.chdir(File.expand_path('..', __FILE__)) do
+    `git ls-files -z 2>#{IO::NULL}`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
+  end
   spec.require_paths = ["lib"]
 
   spec.required_ruby_version = ">= 2.5.0"