diff --git a/payjpv2.gemspec b/payjpv2.gemspec
index be497da..fc9d19b 100644
--- a/payjpv2.gemspec
+++ b/payjpv2.gemspec
@@ -38,8 +38,8 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency 'rspec', '~> 3.6', '>= 3.6.0'
 
-  s.files         = `find *`.split("\n").uniq.sort.select { |f| !f.empty? }
-  s.test_files    = `find spec/*`.split("\n")
+  s.files         = `git ls-files -z`.split("\x0").reject { |f| f.start_with?("spec/", "test/") || f.empty? }
+  s.test_files    = `git ls-files -z -- spec/*`.split("\x0")
   s.executables   = []
   s.require_paths = ["lib"]
 end