diff --git a/actionpack/lib/action_controller/response.rb b/actionpack/lib/action_controller/response.rb
index 5dac4128bbbbf..54a99996ef344 100644
--- a/actionpack/lib/action_controller/response.rb
+++ b/actionpack/lib/action_controller/response.rb
@@ -129,8 +129,8 @@ def assign_default_content_type_and_charset!
 
     def prepare!
       assign_default_content_type_and_charset!
-      set_content_length!
       handle_conditional_get!
+      set_content_length!
       convert_content_type!
     end
 
diff --git a/actionpack/test/controller/render_test.rb b/actionpack/test/controller/render_test.rb
index c4a2bf3db31e9..af7b5dde6284d 100644
--- a/actionpack/test/controller/render_test.rb
+++ b/actionpack/test/controller/render_test.rb
@@ -1321,6 +1321,12 @@ def test_render_against_etag_request_should_304_when_match
     assert @response.body.empty?
   end
 
+  def test_render_against_etag_request_should_have_no_content_length_when_match
+    @request.if_none_match = etag_for("hello david")
+    get :render_hello_world_from_variable
+    assert !@response.headers.has_key?("Content-Length")
+  end
+
   def test_render_against_etag_request_should_200_when_no_match
     @request.if_none_match = etag_for("hello somewhere else")
     get :render_hello_world_from_variable