The 18-year-old singer - who was recently pictured kissing and holding hands with the 'Baby' hitmaker - admitted that she prefers her rumored boyfriend when he's clean-shaven.
When asked whether she minds it when Justin lets his facial fuzz grow she answered: "I actually don't.
"You've got to commit [to growing a mustache]. You can't just be like, 'Let me do a little one.'"
Talking on Sirius XM's radio show 'The Morning Mash', she also gave her opinion on "soul patches" - small areas of hair on the chin - saying she isn't a fan of them either.
She admitted: "I don't like that".
Earlier this week the pretty brunette said she has known the 17-year-old singer for two years and revealed they met through her mother.
She said: "His manager called my mom, who's my manager."
The 'Who Says' star won't confirm whether she and Justin are in a relationship or not but was happy to admit that she is close to him because he "understands" the pressures of fame.
She told talk show host David Letterman: "I'm blushing! He's been in my life for so long and it's just nice to have someone that understands what you're going through."
