Avoid Grievous Injury

Level: 1 divination
Classes: Bard, Cleric, Druid, Sorcerer, Warlock, Wizard
Casting Time: 1 reaction, which you take when you are struck by a critical hit
Range: Self
Components: V, S
Duration: Instantaneous
Source: Deep Magic 5e

You cast this spell when a foe strikes you with a critical hit but before damage dice are rolled. The critical hit against you becomes a normal hit.