diff --git lib/webrick/httpresponse.rb lib/webrick/httpresponse.rb
index e897e8c..ab35677 100644
--- lib/webrick/httpresponse.rb
+++ lib/webrick/httpresponse.rb
@@ -137,6 +137,7 @@ 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