diff --git a/snippets/intersectionBy.md b/snippets/intersectionBy.md
index 3f28a78be..95ad8ffc7 100644
--- a/snippets/intersectionBy.md
+++ b/snippets/intersectionBy.md
@@ -6,7 +6,7 @@ Create a `Set` by applying `fn` to all elements in `b`, then use `Array.filter()
 
 ```js
 const intersectionBy = (a, b, fn) => {
-  const s = new Set(b.map(x => fn(x)));
+  const s = new Set(b.map(fn));
   return a.filter(x => s.has(fn(x)));
 };
 ```
diff --git a/test/intersectionBy/intersectionBy.js b/test/intersectionBy/intersectionBy.js
index 0d598f30b..0a6684fce 100644
--- a/test/intersectionBy/intersectionBy.js
+++ b/test/intersectionBy/intersectionBy.js
@@ -1,5 +1,5 @@
 const intersectionBy = (a, b, fn) => {
-  const s = new Set(b.map(x => fn(x)));
+  const s = new Set(b.map(fn));
   return a.filter(x => s.has(fn(x)));
 };
 module.exports = intersectionBy;