Iran’s currency rose on Wednesday, going below the important threshold of 300,000 rials to one US dollar as optimism increased about the prospects of a nuclear deal.

The rial was trading just below 300,000 in Tehran’s unofficial exchange market for the first time since mid-May. The rial had fallen to as low as 330,000 a few weeks ago as hopes for a nuclear agreement with the United States were fading.

Iran responded to a European Union proposal to resolve the nuclear issue on Monday, in what seemed to offer the best chance since March to reach an agreement.

Iran’s currency began falling in early 2018 when signs emerged that former President Donald Trump was planning to withdraw from the 2015 nuclear agreement and possibly impose sanctions on Iran.

Once the US announced its withdrawal and imposed crippling oil export and banking sanctions, the currency gradually fell ninefold by 2021.

The rial has fallen 4,500-fold since the 1979 revolution that toppled the monarch. The currency was trading at 70 against the dollar in 1978 compared with 3,300 in 2017 and around 300,000 now.

Economists in Tehran have said in recent days that even if a nuclear deal is reached, the rial will not recoup most of its losses and will probably trade at around 240,000 to the dollar, because of serious structural economic issues.