diff --git a/exercises/practice/prism/.meta/proof.ci.ts b/exercises/practice/prism/.meta/proof.ci.ts
index c8d68f967..6d1f42201 100644
--- a/exercises/practice/prism/.meta/proof.ci.ts
+++ b/exercises/practice/prism/.meta/proof.ci.ts
@@ -17,7 +17,7 @@ export const findSequence = (start: Point, prisms: Prism[]): number[] => {
     const dirX = Math.cos(rad)
     const dirY = Math.sin(rad)
 
-    let nearest: Prism
+    let nearest: Prism | undefined
     let nearestDist = Infinity
 
     for (const prism of prisms) {