diff --git a/actionpack/lib/action_dispatch/middleware/ssl.rb b/actionpack/lib/action_dispatch/middleware/ssl.rb
index 68ced4e40c..8d5ab19f60 100644
--- a/actionpack/lib/action_dispatch/middleware/ssl.rb
+++ b/actionpack/lib/action_dispatch/middleware/ssl.rb
@@ -57,7 +57,7 @@ module ActionDispatch
           cookies = cookies.split("\n")
 
           headers['Set-Cookie'] = cookies.map { |cookie|
-            if cookie !~ /;\s+secure(;|$)/
+            if cookie !~ /;\s+secure(;|$)/i
               "#{cookie}; secure"
             else
               cookie
diff --git a/actionpack/test/dispatch/ssl_test.rb b/actionpack/test/dispatch/ssl_test.rb
index 881a8474e1..61b55f3d82 100644
--- a/actionpack/test/dispatch/ssl_test.rb
+++ b/actionpack/test/dispatch/ssl_test.rb
@@ -124,6 +124,20 @@ class SSLTest < ActionDispatch::IntegrationTest
       response.headers['Set-Cookie'].split("\n")
   end
 
+  def test_flag_cookies_as_secure_with_ignore_case
+    self.app = ActionDispatch::SSL.new(lambda { |env|
+      headers = {
+        'Content-Type' => "text/html",
+        'Set-Cookie' => "problem=def; path=/; Secure; HttpOnly"
+      }
+      [200, headers, ["OK"]]
+    })
+
+    get "https://example.org/"
+    assert_equal ["problem=def; path=/; Secure; HttpOnly"],
+      response.headers['Set-Cookie'].split("\n")
+  end
+
   def test_no_cookies
     self.app = ActionDispatch::SSL.new(lambda { |env|
       [200, {'Content-Type' => "text/html"}, ["OK"]]