Costco’s switch from American Express to Visa is being pushed back to this summer.

Costco Wholesale had previously announced that the switch in the only credit card it will accept in its U.S. stores would happen in April.

It’s now saying that transition will happen in June or by midsummer.

For years, American Express had been the Seattle-area retail giant’s credit card network and the issuer of its co-branded credit cards.

But last year Costco said it had struck a deal with Visa to replace American Express as its credit-card network, and for Citigroup to become the exclusive issuer of its co-branded credit cards.

The original contract with American Express ends March 31 this year but “our plan is to extend that” by a few months until the Citigroup deal kicks in, said Richard Galanti, Costco’s chief financial officer.

The timing of the transition “is fluid,” Galanti said. “It’s between Amex and Citi — negotiating and completing the agreements to do that transition.”

Once the transition occurs, Costco will accept all Visa credit cards at its U.S. stores, Galanti said.