The governor of Sweden’s central bank compared buying and selling Bitcoins to trading stamps, questioning the staying power of currencies without government backing, Bloomberg reports.

“Private money usually collapses sooner or later,” Riksbank Governor Stefan Ingves said at a banking conference in Stockholm. “And sure, you can get rich by trading in bitcoin, but it’s comparable to trading in stamps”.

While Bitcoin has gained from endorsements by the likes of Elon Musk and Cathie Wood of Ark Investment Management, some central bankers have compared to the tulip bubble of the 17th century, which ended in collapse.

Ingves said earlier this year that Bitcoin and other cryptocurrencies are unlikely to escape regulatory oversight as their popularity grows.