Annuity rates, which determine the value of a private pension pot, experienced their biggest monthly fall for three years in August, according to Investment Life and Pensions Moneyfacts.
The information firm found that the figures show that the average annual income from a typical standard annuity for a 65-year-old, based on a £50,000 ($81,013, €62,746.) pension pot, fell by 2.6% in August, meaning the average income fell from £2,874 to £2,797.
That may not sound like much to worry about, but over a 20-year retirement this equates to £1,540 less income.
It also represents the biggest monthly fall in annuity income since August 2011, and leaves annuity income down by 3.2% since the start of the year.
"A fall in annuity rates of the magnitude that we saw in August is unusual, but a significant reduction in gilt yields combined with falling demand has left annuity providers with little room for manoeuvre," said Richard Eagling, head of pensions at Investment Life and Pensions Moneyfacts.
"These are testing times for the annuity market and we expect that pricing annuities will remain challenging until the new pension freedoms are introduced next April.
"Although many individuals approaching retirement will be looking to postpone their decision on how to take a retirement income until then, the significant fall in annuity income that we saw last month will be felt by those who require a guaranteed, secure income now."
The study also found that enhanced annuities saw a much smaller reduction of 1.3%, as the table below shows, but enhanced annuity rates have fallen much more steeply than standard rates in previous months.
The findings come after the Chancellor George Osborne announced a range of radical pension reforms in his 2014 Budget.
The Conservative MP said, among other things, that savers would be able to take out their pension pot without buying an annuity.