How to prevent my iPhone from charging my Mac?

I often leave my phone plugged into my MacBook over night. After switching to an iPhone with USB-C, it started charging up my Mac from the phone battery if the Mac isn't connected to power, which results in my phone being dead in the morning. I'm unsure whether the Mac's battery is already flat when this happens, or if it happens when the Mac is still sleeping. The battery settings on the iPhone show power being used by "USB-C Accessories". Is there any way to disable this reverse charging behaviour?