Sweden'sgovernment has an unusual complaint — it is collecting too much tax.
Negative interest rates have made some of the world's highest taxes a lot less painful as businesses and individuals race to hand cash to the state because of the relatively generous returns on offer.
Data released on Wednesday showed Sweden's government generated a budget surplus of SKr85bn ($9.5bn) in 2016, with approximately SKr40bn coming from tax overpayments. The government will have to repay more than £3.5bn to businesses and individuals who purposely paid too much tax in 2016.
The government wants to discourage further overpayments but the national debt office has admitted its efforts will probably not be enough.
"We cannot do anything [further], it is simply a consequence of current interest rates," Marten Bjellerup, the office's head of forecasting, said on Wednesday.
The payments are an unintended consequence of the Swedish central bank's efforts to kick-start inflation in the local economy by lowering interest rates to below zero per cent two years ago.
While bank interest rates plummeted, Swedish tax rules meant that excess deposits in taxpayers' payment accounts continued to earn a minimum of 0.56 per cent annual interest, leading many people to use them like makeshift bank accounts.
Most governments would be pleased with an annual budget surplus more than twice the forecast size. But Stockholm has complained that this "involuntary borrowing" from residents will cost it around SKr800m more over 2016 and 2017 than if they had borrowed the money at market rates.
The ballooning surplus follows a similar boost to income for the federal government in Switzerland, which introduced negative rates in 2015. Olle Holmgren, chief strategist for Sweden at SEB, said the unpredictable overpayments "create a bit of a problem for the debt office".
He said: "They don't know how long the payments will stay in the account, which means that if these funds are withdrawn they will have to find funding elsewhere. It can be handled but it creates a new element of uncertainty in the budget and borrowing process."
The government has now removed interest payments on tax deposits but the national debt office expects that even a zero per cent interest rate will remain attractive for businesses. The Stockholm interbank offered rate, which the debt office uses as a proxy for the interest rates paid by companies, has been negative since March 2015.
Mr Holmgren said a number of SEB's corporate clients "have indicated that they intend to keep higher surpluses on their tax accounts after the change has been made".
Unfortunately for the debt office there is little chance that the problem will go away any time soon. At its latest policy meeting last week the central bank said it was more likely to cut rates further into negative territory than increase them in the short term.