The issue dominated much of the G7 finance chiefs meeting in Japan.
Dimon claimed any technical default could cause financial panic and JPMorgan had convened a 'war room' internally to deal with the issue.
"It's very unfortunate, it's time-consuming, hopefully it won't happen, but it affects contracts, collateral, clearing houses, clients," Dimon said.
Chinese stocks underperformed, with the G7 meeting mulling restrictions on investment to the world's second-biggest economy.
Bank of England chief economist Huw Pill speaksReuters GraphicsJobless claimsReuters GraphicsReuters GraphicsBy Mike Dolan, editing by Christina Fincher, <a href="mailto:mike.dolan@thomsonreuters.com" target="_blank">mike.dolan@thomsonreuters.com</a>.