Shorter way to conditionally "return ()" in a monad chain (>>, >>=) in Haskell?

Shorter way to conditionally "return ()" in a monad chain (>>, >>=) in
Haskell?

I have this simple code which reads a string and prints it, indefinitely.
main :: IO ()
main = getLine >>= putStrLn >> main
Now I want to exit after the getLine call if the line is either "quit" or
"exit".
My attempt:
main :: IO ()
main = do
line <- getLine
if line == "exit" || line == "quit"
then return ()
else putStrLn line >> main
Doesn't look idiomatic to me. Is there a better way?