GarageBand is trying to record audio with my headphones

When I record audio for the sampler in GarageBand, I have to unplug my headphones, because it's trying to use them to record audio.

When I go to record, it says, "Record a sound using the device connected to the headphones jack, then instantly play it on the Sampler keyboard."

That's not gonna work, because my headphones can't record. And as I'd expect, when I try to record something with them plugged in, absolutely nothing happens.