Bitcoin, the original stateless cryptocurrency, has often been tolerated and sometimes embraced by governments, central banks, and other key institutions around the world. But there is a limit to some officials’ acceptance of cryptoassets.

The president of the European Central Bank yesterday rejected the idea that Estonia, which is part of the euro zone, could issue and manage its own state-backed cryptocurrency. The idea is still theoretical, but ECB president Mario Draghi shot it down anyway when asked about it at a press conference: “No member state can introduce its own currency; the currency of the euro zone is the euro.”

An Estonian cryptocurrency has been mooted as part on the country’s e-Residency program that provides a digital identity to foreign entrepreneurs. Kaspar Korjus, managing director at e-Residency, floated the idea of issuing ”estcoins” that allow people to invest in the country. The cryptocurrency would be available through its its e-residency program via an initial coin offering, which takes some of the principles of bitcoin and blends them with crowdfunding. Proceeds could go into a type of public-private partnership.

Last week, China’s central bank said fundraising through digital tokens—that is, initial coin offerings—was illegal, a move that sent shockwaves through the burgeoning token markets.

Meanwhile the euro has been on a tear lately, rallying against fellow old-school fiat currencies of just about every major trading partner amid the region’s economic recovery. The common currency has gained nearly 15% against the dollar so far this year. Over that same period against the greenback, bitcoin is up nearly 400%.