The chief economist for financial services giant UBS came out against bitcoin and cryptocurrencies in a big way on Twitter last week.

In a series of tweets on Nov. 1 and 2, UBS global chief economist Paul Donovan compared bitcoin to the Netherland’s 1637 tulip crisis, the Weimar Republic’s hyperinflation and PetSmart. His remarks came after derivatives powerhouse CME Group revealed its intention to list a bitcoin futures contract later this year.

Donovan’s most forceful objection to bitcoin came from the tulip analogy:

“Amsterdam 1636. Cash-settled futures markets in tulip bulbs start. Prices soar. Amsterdam February 1637. Tulip bubble bursts #beenherebefore”

Though Donovan compared the bitcoin bubble to the tulip mania, he stated in a follow-up tweet that the economic impact would likely differ. And in an email to CNBC, he said that the idea of not delivering a product was “shocking” at the time. People picked up and traded tulip bulbs in taverns, which he likened to today’s cryptocurrency exchanges.

While Donovan opposes cryptocurrencies, he did say that he was a “big fan of blockchain” on Twitter. In another tweet, he said UBS thinks of blockchain as a platform which should continue to grow.

Donovan is not the first to compare bitcoin’s astonishing price increases to the tulip crisis. JP Morgan Chase CEO Jamie Dimon infamously called the cryptocurrency a “fraud” in September, saying it was worse than the 17th century tulip crisis.

Paul Donovan image via Youtube