Wall Street pioneer Thomas Peterffy told CNBC on Wednesday that he was concerned about the prospect of damaging inflation in the US, based on his personal experiences as a youth in Hungary after World War II.

The founder and chairman of billionaire Interactive Brokers commented on “Squawk Box” shortly after the consumer price index data was released in April.

“Whenever I hear numbers like this, I look back on my childhood in Hungary, where I played with … billions of forint notes. So the value of money meant nothing,” said Peterffy, who emigrated from Hungary to the United States in 1965 The forint is Hungary’s official currency.

“I am very concerned that this is an unstoppable situation because the longer the Fed waits, the more they have to raise rates,” added Peterffy, which in turn could make servicing the US national debt more difficult. “So we’re basically painting ourselves in a box and I don’t see how we’re going to get out of there.”

According to the Ministry of Labor, the consumer price index rose by 4.2% in April compared to the previous year. That headline gain for CPI, which measures a range of goods, energy and housing costs, is the fastest in more than 12 years.

The jump comes as the continued rollout of Covid vaccinations helps the U.S. economy recover from the pandemic.

One factor to consider when interpreting April CPI data is that year-on-year comparisons will be affected by the occurrence of the coronavirus pandemic in 2020. The health crisis and its economic impact caused consumer prices to fall by the largest amount since December 2008 in April 2020.

As a result, Federal Reserve officials, including Chairman Jerome Powell, have indicated that inflation would look higher this spring due to so-called base effects. Even so, Wednesday’s CPI data showed a 0.8% month-on-month increase, much higher than economists’ expected 0.2%.

Powell has repeatedly insisted that he believes that price hikes during the recovery of Covid will be temporary, rather than the start of problematic runaway inflation like the US did in the 1960s and 1970s. Because of this, Powell and other central bankers continue to feel the need to maintain highly accommodative monetary policies in response to the pandemic.

“We’re not quite out of the pandemic yet,” James Bullard, president of the St. Louis Federal Reserve, told CNBC on Tuesday. “Once we’re out of the pandemic, I think it will be time to see if monetary policy can change.”

Peterffy isn’t the only person who disagrees with the Fed’s current approach. Billionaire investor Stanley Printmiller tore the central bank on CNBC Tuesday, suggesting the US dollar’s long-term health is at stake.

“I can’t find a period in history when monetary and fiscal policy was inconsistent with economic circumstances, not one,” said Druckermiller.

– CNBC’s Jeff Cox contributed to this report.