diff --git a/examples/rack/config.ru b/examples/rack/config.ru
index 4b36b777..e545444f 100755
--- a/examples/rack/config.ru
+++ b/examples/rack/config.ru
@@ -11,9 +11,9 @@ srand
 app = lambda do |_|
   case rand
   when 0..0.8
-    [200, { 'Content-Type' => 'text/html' }, ['OK']]
+    [200, { 'content-type' => 'text/html' }, ['OK']]
   when 0.8..0.95
-    [404, { 'Content-Type' => 'text/html' }, ['Not Found']]
+    [404, { 'content-type' => 'text/html' }, ['Not Found']]
   else
     raise NoMethodError, 'It is a bug!'
   end