diff --git a/.gitignore b/.gitignore
index 48b8bf9..7b5c283 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 vendor/
+.bundle/
diff --git a/Gemfile.lock b/Gemfile.lock
index ea857ad..c450ff2 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,12 +6,33 @@ PATH
 GEM
   remote: http://rubygems.org/
   specs:
+    ast (2.4.2)
+    parallel (1.22.1)
+    parser (3.1.2.0)
+      ast (~> 2.4.1)
+    rainbow (3.1.1)
+    regexp_parser (2.4.0)
+    rexml (3.2.5)
+    rubocop (1.29.1)
+      parallel (~> 1.10)
+      parser (>= 3.1.0.0)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.17.0, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 1.4.0, < 3.0)
+    rubocop-ast (1.18.0)
+      parser (>= 3.1.1.0)
+    ruby-progressbar (1.11.0)
+    unicode-display_width (2.1.0)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
   format-staged!
+  rubocop (~> 1.29)
 
 BUNDLED WITH
    2.1.4
diff --git a/format-staged.gemspec b/format-staged.gemspec
index df36505..0ab79ad 100644
--- a/format-staged.gemspec
+++ b/format-staged.gemspec
@@ -13,4 +13,6 @@ Gem::Specification.new do |s|
   s.executables << 'git-format-staged'
   s.homepage    = 'https://github.com/5sw/format-staged'
   s.license     = 'MIT'
+  
+  s.add_development_dependency 'rubocop', '~> 1.29'
 end