ASB still expected the central bank to remain on hold at 1.75% until late next year.
The 0.4% fall in both total and core spending was in line with ASB forecasts but higher than the market expected, he said.
''We anticipated the fall based on the fact both consumables and durables spending was very buoyant over April.''
As a result, some payback was due. Consumables spending, such as items bought at a supermarket, dipped 0.7% and durables spending was flat during the month.
Annual spending growth was 5.2%, Statistics New Zealand data showed.
Card spending was expected to lift in June and July because of the British and Lions rugby tour.
Mr Tuffley said hospitality spending fell 0.8% in May when another firm result had been expected.
The fall might have been due to a ''temporary hangover'' following the departure of athletes from the World Masters Games.
Looking through the monthly volatility, spending growth remained moderate, albeit back from 2016 highs, he said.
''From here, we expect spending to continue at similar levels over the remainder of 2017.''
With that in mind, high population growth, improving dairy incomes, along with improved consumer confidence, were being offset by a more subdued housing market and the late-2016 lending interest rate increases, he said.
