diff --git a/src/boot/boot.janet b/src/boot/boot.janet
index c6d48bcd..96ed9465 100644
--- a/src/boot/boot.janet
+++ b/src/boot/boot.janet
@@ -73,6 +73,7 @@
   nil)
 
 # Basic predicates
+(defn nan? "Check if x is NaN" [x] (not= x x))
 (defn even? "Check if x is even." [x] (== 0 (% x 2)))
 (defn odd? "Check if x is odd." [x] (not= 0 (% x 2)))
 (defn zero? "Check if x is zero." [x] (== x 0))