ESP-01 D1 pinMode

I'm not able to use pin D1 on my ESP8266 ESP-01 module. It's hooked up to the on-board LED, and I'd like to use it as a status indicator, but any attempts to read from or write to that pin cause Espruino to crash. All the other pins are working properly.

Is this pin unavailable since it's connected to something else internally? Am I forgetting something simple?

To reproduce the issue, simply connect to the blank ESP-01 and run

digitalWrite(1,0);