diff --git a/snippets/intersectionBy.md b/snippets/intersectionBy.md
index 8c7d43390..958c18b11 100644
--- a/snippets/intersectionBy.md
+++ b/snippets/intersectionBy.md
@@ -10,10 +10,10 @@ Create a `Set` by applying `fn` to all elements in `b`, then use `Array.prototyp
 ```js
 const intersectionBy = (a, b, fn) => {
   const s = new Set(b.map(fn));
-  return a.filter(x => s.has(fn(x)));
+  return [...new Set(a)].filter(x => s.has(fn(x)));
 };
 ```
 
 ```js
 intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [2.1]
-```
\ No newline at end of file
+```