--- a/rmagick.gemspec
+++ b/rmagick.gemspec
@@ -13,7 +13,7 @@
   s.homepage = 'https://github.com/rmagick/rmagick'
   s.license = 'MIT'
 
-  tracked_files = `git ls-files`.split($OUTPUT_RECORD_SEPARATOR)
+  tracked_files = Dir['deprecated/*', 'ext/**/*', 'lib/**/*', '*.gemspec']
   file_exclusion_regex = %r{\A(doc|benchmarks|examples|spec|lib/rvg/to_c.rb)}
   files         = tracked_files.reject { |file| file[file_exclusion_regex] }
   test_files    = files.grep(%r{^(test|spec|features)/})