diff --git lib/webrick/httpresponse.rb lib/webrick/httpresponse.rb
index e897e8c..e20974e 100644
--- lib/webrick/httpresponse.rb
+++ lib/webrick/httpresponse.rb
@@ -181,7 +181,11 @@ module WEBrick
     # Will this response body be returned using chunked transfer-encoding?
 
     def chunked?
-      @chunked
+      if @header['transfer-encoding'] == 'chunked'
+        @chunked = true
+      else
+        @chunked
+      end
     end
 
     ##
diff --git test/webrick/test_httpresponse.rb test/webrick/test_httpresponse.rb
index 1f85a92..81b1268 100644
--- test/webrick/test_httpresponse.rb
+++ test/webrick/test_httpresponse.rb
@@ -47,6 +47,16 @@ module WEBrick
       assert_equal 0, logger.messages.length
     end
 
+    def test_200_chunked_does_not_set_content_length
+      res.body        = 'hello'
+      res.status      = 200
+      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'