diff --git a/lib/webrick/httpresponse.rb b/lib/webrick/httpresponse.rb
index 9942a59714..ba4494ab74 100644
--- a/lib/webrick/httpresponse.rb
+++ b/lib/webrick/httpresponse.rb
@@ -155,6 +155,7 @@ module WEBrick
     # Sets the response header +field+ to +value+
 
     def []=(field, value)
+      @chunked = value.to_s.downcase == 'chunked' if field.downcase == 'transfer-encoding'
       @header[field.downcase] = value.to_s
     end
 
diff --git a/test/webrick/test_httpresponse.rb b/test/webrick/test_httpresponse.rb
index 696163ba18..e8c69a1212 100644
--- a/test/webrick/test_httpresponse.rb
+++ b/test/webrick/test_httpresponse.rb
@@ -133,6 +133,13 @@ module WEBrick
       assert_equal 0, logger.messages.length
     end
 
+    def test_200_chunked_does_not_set_content_length
+      res.chunked     = false
+      res["Transfer-Encoding"] = 'chunked'
+      res.setup_header
+      assert_nil res.header.fetch('content-length', nil)
+    end
+
     def test_send_body_io
       IO.pipe {|body_r, body_w|
         body_w.write 'hello'