diff --git a/src/steps/three.ts b/src/steps/three.ts
index e76253a..05e563c 100644
--- a/src/steps/three.ts
+++ b/src/steps/three.ts
@@ -6,7 +6,10 @@ const adder = overload([
         throw new TypeError('Can only add numbers')
     },
     (x: string, y: string) => 'Yay' + x + y
-])
+] as const)
 
 console.log(adder(1, 2))
 console.log(adder('a', 'b'))
+//@ts-expect-error
+console.log(adder(3n, 4n))
+