Consumer prices fell 0.1% from a year ago in May, according to the country’s statistics office. That outcome was down from zero in April and matched the median estimate in a Bloomberg survey of economists.

The switch to outright disinflation reflects the strength of the franc, which has made imports so cheap that the foreign contribution to prices has already been negative for several months. That increases the onus to respond on the Swiss National Bank, which is widely expected to cut borrowing costs to zero on June 19.

Inflation was pushed down by heating oil and air transport, while rents and some fruit and vegetable costs rose, the government agency said Tuesday. The core gauge, which excludes fresh and seasonal products as well as energy, slowed to 0.5%.

While President Martin Schlegel has said repeatedly that the economy may experience individual months of negative inflation, he’s also cautioned as recently as last week that such outcomes won’t necessarily trigger a central-bank reaction. 

“Our focus is not on the current rate of inflation, but rather on price stability over the medium term,” he said last week. Fellow policymaker Petra Tschudin may face questions on the matter after a speech later Tuesday.

A 25 basis-point cut is fully priced in for this month, following five prior steps totaling 150 basis points so far. That move would bring the interest rate to zero. Some economists even anticipate a return to negative borrowing costs, though only a minority expects that to come already at the upcoming meeting. 

Since the financial crisis of 2008, there were four periods where Swiss inflation was below zero for several months. The SNB targets a range of 0%-2%.

Consumer-price growth in the surrounding euro area remains significantly stronger than in Switzerland, and is anticipated to have been 2% in May.  Based on the European Union’s harmonized measure, Swiss prices saw a drop of 0.2% in the period.