diff --git a/actionpack/lib/action_controller/base.rb b/actionpack/lib/action_controller/base.rb
index 9b4b729e8d..288e6d2912 100755
--- a/actionpack/lib/action_controller/base.rb
+++ b/actionpack/lib/action_controller/base.rb
@@ -1087,7 +1087,11 @@ module ActionController #:nodoc:
 
       def assign_default_content_type_and_charset
         response.content_type ||= Mime::HTML
-        response.charset      ||= self.class.default_charset
+        response.charset      ||= self.class.default_charset unless sending_file?
+      end
+
+      def sending_file?
+        response.headers["Content-Transfer-Encoding"] == "binary"
       end
 
       def action_methods
diff --git a/actionpack/test/controller/send_file_test.rb b/actionpack/test/controller/send_file_test.rb
index a4617cbf5a..83590fd73e 100644
--- a/actionpack/test/controller/send_file_test.rb
+++ b/actionpack/test/controller/send_file_test.rb
@@ -63,6 +63,14 @@ class SendFileTest < Test::Unit::TestCase
     assert_equal file_data, response.body
   end
 
+  def test_headers_after_send_shouldnt_include_charset
+    response = process('data')
+    assert_equal "application/octet-stream", response.headers["Content-Type"]
+
+    response = process('file')
+    assert_equal "application/octet-stream", response.headers["Content-Type"]
+  end
+
   # Test that send_file_headers! is setting the correct HTTP headers.
   def test_send_file_headers!
     options = {