diff --git a/.rubocop.yml b/.rubocop.yml
index 576f1c2..c8c3cab 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,3 +1,6 @@
+Metrics/AbcSize:
+  Max: 16
+
 Metrics/BlockNesting:
   Max: 1
 
diff --git a/Gemfile b/Gemfile
index 5744b42..8a27421 100644
--- a/Gemfile
+++ b/Gemfile
@@ -9,7 +9,7 @@ group :test do
   gem 'mime-types', '~> 1.25', :platforms => [:jruby, :ruby_18]
   gem 'rest-client', '~> 1.6.0', :platforms => [:jruby, :ruby_18]
   gem 'rspec', '>= 2.14'
-  gem 'rubocop', '>= 0.25', :platforms => [:ruby_19, :ruby_20, :ruby_21]
+  gem 'rubocop', '>= 0.28', :platforms => [:ruby_19, :ruby_20, :ruby_21]
   gem 'simplecov', '>= 0.9'
   gem 'yardstick'
 end
diff --git a/lib/simple_oauth/header.rb b/lib/simple_oauth/header.rb
index 0c2d5e8..fdeb4b3 100644
--- a/lib/simple_oauth/header.rb
+++ b/lib/simple_oauth/header.rb
@@ -87,7 +87,7 @@ module SimpleOAuth
       matching_keys, extra_keys = options.keys.partition { |key| ATTRIBUTE_KEYS.include?(key) }
       extra_keys -= IGNORED_KEYS
       if options[:ignore_extra_keys] || extra_keys.empty?
-        Hash[options.select { |key, _value| matching_keys.include?(key) }.collect { |key, value| [:"oauth_#{key}", value] }]
+        Hash[options.select { |key, _| matching_keys.include?(key) }.collect { |key, value| [:"oauth_#{key}", value] }]
       else
         fail "SimpleOAuth: Found extra option keys not matching ATTRIBUTE_KEYS:\n  [#{extra_keys.collect(&:inspect).join(', ')}]"
       end