diff --git a/docs/guide/custom-extensions.md b/docs/guide/custom-extensions.md
index 2e5f6a71..5abe3128 100644
--- a/docs/guide/custom-extensions.md
+++ b/docs/guide/custom-extensions.md
@@ -441,7 +441,7 @@ const CustomExtension = Extension.create({
   onUpdate() {
     // The content has changed.
   },
-  onSelectionUpdate({editor}) {
+  onSelectionUpdate({ editor }) {
     // The selection has changed.
   },
   onTransaction({ transaction }) {