Josipovic declined to say whether changing the law would be the most fortunate solution, adding that there was still time for consultations.
Alongside protection of national interests, the Croatian authorities must honour the signed agreements, according to the president.
In addition, the law should be protected and it also should be established if there was corruption in this case, he said.
According to Josipovic, Hungarian Prime Minister Viktor Orban is protecting Hungary's interests and it is up to Croatian authorities to protect the law.
"If there was corruption, it should be investigated and proved by the judiciary. Until then, ways should be found to safeguard Croatia's interests," he said during a visit to the northern town of Donji Kraljevec.
As for a referendum on Croatia's EU membership, Josipovic called for separating EU topics from the campaign for the forthcoming parliamentary elections.
A consensus must be reached by the parties that advocate EU membership, he said calling on the parliament to decide on a realistic date for the referendum and on the next government to convince Croatians about the advantages of EU membership.