diff --git a/documentation/docs/07-misc/01-best-practices.md b/documentation/docs/07-misc/01-best-practices.md
index 1afba7a8c8..02c97af185 100644
--- a/documentation/docs/07-misc/01-best-practices.md
+++ b/documentation/docs/07-misc/01-best-practices.md
@@ -16,6 +16,8 @@ To compute something from state, use `$derived` rather than `$effect`:
 
 ```js
 // @errors: 2451
+declare let num: number;
+// ---cut---
 // do this
 let square = $derived(num * num);