diff --git a/actionpack/lib/action_dispatch/testing/test_request.rb b/actionpack/lib/action_dispatch/testing/test_request.rb
index d0beb72a410d56d682c9c2b76a2acff31f990940..91b25ec1552f802a443d36a11f4fbf14fe4dfac7 100644
--- a/actionpack/lib/action_dispatch/testing/test_request.rb
+++ b/actionpack/lib/action_dispatch/testing/test_request.rb
@@ -22,7 +22,7 @@ def self.default_env
     private_class_method :default_env
 
     def request_method=(method)
-      set_header("REQUEST_METHOD", method.to_s.upcase)
+      super(method.to_s.upcase)
     end
 
     def host=(host)
diff --git a/actionpack/test/dispatch/test_request_test.rb b/actionpack/test/dispatch/test_request_test.rb
index 35af3076ba79e6abf7b049d21668f50738260501..b479af781d7b031caea99d72c756dfe1850e4c6b 100644
--- a/actionpack/test/dispatch/test_request_test.rb
+++ b/actionpack/test/dispatch/test_request_test.rb
@@ -88,6 +88,13 @@ class TestRequestTest < ActiveSupport::TestCase
     assert_equal "GoogleBot", req.user_agent
   end
 
+  test "request_method getter and setter" do
+    req = ActionDispatch::TestRequest.create
+    req.request_method # to reproduce bug caused by memoization
+    req.request_method = "POST"
+    assert_equal "POST", req.request_method
+  end
+
   test "setter methods" do
     req = ActionDispatch::TestRequest.create({})
     get = "GET"