The European Union spent about 5.5 billion euros (6.1 billion dollars) of its 2015 budget in error, the bloc's auditing body announced Thursday, while warning of a loss in citizens' trust.
The European Court of Auditors' (ECA) annual report comes at a time of soul-searching across the EU, following Britain's shock decision to leave the bloc, which is seen in part as a manifestation of broader euroscepticism.
"People cannot even begin to trust the EU institutions if they do not believe we are looking after their money properly and keeping a good account of how we are doing that," said ECA chief Klaus-Heiner Lehne.
The irregularities affected 3.8 per cent of the EU's budget for 2015, down from a 4.4-per-cent error rate the previous year.
The auditing court would like to see a rate of less than 2 per cent.
The Luxembourg-based watchdog said that - as in the previous year - the most errors were found in regional aid granted to EU member states and in spending meant to boost growth and job-creation, which are both priority areas for the bloc.
EU member states and the bloc's executive, the European Commission, corrected some of the irregularities, preventing the error rate from reaching 5.5 per cent, the court found.
But "more errors could have been corrected," it said in a statement, calling on the commission to make "full use" of its powers to reduce errors further and recover misspent funds.