diff --git a/.document b/.document
new file mode 100644
index 0000000..e5a784f
--- /dev/null
+++ b/.document
@@ -0,0 +1,4 @@
+LICENSE.txt
+README.md
+ext/io/console/console.c
+lib/io/console/size.rb
diff --git a/.gitignore b/.gitignore
index 153aded..98df0f5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 /coverage/
+/doc/
 /pkg/
 /tmp/
 /logs/
diff --git a/io-console.gemspec b/io-console.gemspec
index d26a757..8f12c53 100644
--- a/io-console.gemspec
+++ b/io-console.gemspec
@@ -13,6 +13,7 @@ Gem::Specification.new do |s|
   s.authors = ["Nobu Nakada"]
   s.require_path = %[lib]
   s.files = %w[
+    .document
     LICENSE.txt
     README.md
     ext/io/console/console.c