"I am very glad that I am doing what I promised at the very beginning of my presidency, ...namely supporting Polish families, protecting Polish children," Duda said after signing the draft amendment.
The motion is expected to sail through the lower house of the Polish parliament, run by the ruling Law and Justice party that nominated Duda for a second term, putting him on a collision course with Brussels. Duda has argued that over 70 percent of Poles oppose placing kids with homosexual foster parents.
Same-sex marriage is not recognized in Poland, but no laws are preventing gay people from adopting children. Duda, who will go into the second round of presidential voting this Sunday, wants to close that loophole.