BERLIN (AP) — Luxembourg's prime minister is criticizing the Polish president's campaign against LGBT rights in the run-up to a closely fought runoff election this weekend.

Polish President Andrzej Duda, a nationalist conservative, recently has called LGBT rights an “ideology” more dangerous than communism, and on Monday formally proposed a constitutional amendment to bar same-sex couples from adopting children.

Luxembourg Prime Minister Xavier Bettel married his partner in 2015, a year after his Roman Catholic nation approved a law allowing same-sex marriage.

“Apparently one sometimes says things one shouldn't say during election campaigns,” German weekly Der Spiegel quoted Bettel as saying in an interview on Friday. “I won't forget them.”

“I was quite surprised by what Mr. Duda said,” he added. “I have met him several times; he even invited me to Poland together with my husband.”

Duda faces a tough challenge from liberal Warsaw Mayor Rafal Trzaskowski as he seeks a second five-year term. The first round in late June eliminated nine other candidates, leaving the two rivals to fight out Sunday's runoff vote.

While Duda has made his opposition to LGBT rights a key campaign theme, Trzaskowski signed a tolerance declaration last year that triggered a backlash against gay rights in mostly Catholic Poland.

Duda and the governing Law and Justice party, which supports him, have won the backing of older and rural Poles, helped by cash payments to families and other welfare programs.