I finally got it to work with onResponse : I traced each possible response to see which one was fired when clicking the close button.... onResponse aboutdialog $ \resp -> do putStrLn "onResponse!!!" case resp of ResponseNone -> putStrLn "ResponseNone" ResponseReject -> putStrLn "ResponseReject" ResponseAccept -> putStrLn "ResponseAccept" ResponseDeleteEvent -> putStrLn "ResponseDeleteEvent" ResponseOk -> putStrLn "ResponseOk" ResponseCancel -> putStrLn "ResponseCancel" >> widgetHide aboutdialog ResponseClose -> putStrLn "ResponseClose" ResponseYes -> putStrLn "ResponseYes" ResponseNo -> putStrLn "ResponseNo" ResponseApply -> putStrLn "ResponseApply" ResponseHelp -> putStrLn "ResponseHelp" ResponseUser n -> putStrLn ("ResponseUser "++ show n)