diff --git a/ext/win32/win32-registry.gemspec b/ext/win32/win32-registry.gemspec
index b6df247574..cbac30f221 100644
--- a/ext/win32/win32-registry.gemspec
+++ b/ext/win32/win32-registry.gemspec
@@ -18,7 +18,7 @@ Gem::Specification.new do |spec|
   spec.files = Dir.chdir(__dir__) do
     `git ls-files -z`.split("\x0").reject do |f|
       (File.expand_path(f) == __FILE__) ||
-        f.start_with?(*%w[bin/ test/ spec/ features/ .git .github appveyor Gemfile])
+        f.start_with?(*%w[bin/ test/ spec/ features/ .git .github .mailmap appveyor Gemfile])
     end
   end
   spec.bindir = "exe"