Culture secretary Maria Miller risked the wrath of Tory traditionalists as she spoke passionately about the government's plans for gay marriage.
Ministers are committed to allowing gay people to marry in the same way as straight couples, but many grassroots Tories are opposed to the idea, claiming it contradicts traditional family values.
Miller's defence of the policy sparked a mixed reaction at the conference in Birmingham, with younger activists loudly cheering and applauding, while many older party members sat stony-faced with their arms crossed.
At least two boos could be heard from the floor of the Symphony Hall after Miller said: "Five years ago I stood here and told you that I believed in marriage, and nothing's changed.
"I still believe in marriage - it's part of the bedrock of our society," said Miller, who recently joined many other senior parliamentarians in support the Out4Marriage campaign.
Miller filmed a video in support of the Out4Marriage campaign
"The state should not stop two people from making the commitment to be married unless there's a good reason.
"I don't believe being gay is one of them."
Miller, who is the Cabinet minister responsible for equalities, raised the divisive issue in her keynote speech which centred on the Olympics and Paralympics - widely praised for changing people's perceptions of disability.
Just before bringing up the thorny gay marriage topic, she was applauded as she said: "One undeniable legacy of the Games is that it made us think about disability differently; thinking about what individuals can do, not what they can't - treating each other with respect.
"As a society we have to make sure that gender, sexuality, ethnicity and disability are no barrier to full and equal participation."