Help me convince him.

😀
This is a question for those who didn't find out the gender. 
I am dead set on not knowing the wonder until birth but my boyfriend desperately wants to know. This will be my first and his second child. I have always wanted to be surprised since I was little like my parents. And he found out for his daughter. How can I convince him not to find out? I just think I would catch on if he knew the gender he's horrible at keeping secrets.