diff --git a/lib/rack/contrib/locale.rb b/lib/rack/contrib/locale.rb
index 0dbccc2..9e76dfd 100644
--- a/lib/rack/contrib/locale.rb
+++ b/lib/rack/contrib/locale.rb
@@ -75,7 +75,7 @@ def user_preferred_locale(header)
         matched_locale = I18n.available_locales.find { |al| match?(al, locale) } if locale
         if !locale && !matched_locale
           matched_locale = locales.reverse.find { |locale| I18n.available_locales.any? { |al| variant_match?(al, locale) } }
-          matched_locale = matched_locale[0,2] if matched_locale
+          matched_locale = matched_locale[0,2].downcase if matched_locale
         end
         matched_locale
       else
diff --git a/test/spec_rack_locale.rb b/test/spec_rack_locale.rb
index 2bdfbd8..601fcc7 100644
--- a/test/spec_rack_locale.rb
+++ b/test/spec_rack_locale.rb
@@ -75,6 +75,10 @@ def enforce_available_locales(enforce)
       _(response_with_languages('pt;Q=0.9,es-CL').body).must_equal('es')
     end
 
+    specify 'should match languages with variants case insensitively' do
+      _(response_with_languages('pt;Q=0.9,ES-CL').body).must_equal('es')
+    end
+
     specify 'should skip * if it is followed by other languages' do
       _(response_with_languages('*,dk;q=0.5').body).must_equal('dk')
     end