diff --git a/docs/walkthroughs/03-defining-custom-elements.md b/docs/walkthroughs/03-defining-custom-elements.md
index 8472ea5d8..26ab208fb 100644
--- a/docs/walkthroughs/03-defining-custom-elements.md
+++ b/docs/walkthroughs/03-defining-custom-elements.md
@@ -214,7 +214,7 @@ const App = () => {
             Transforms.setNodes(
               editor,
               { type: match ? 'paragraph' : 'code' },
-              { match: n => Editor.isBlock(editor, n) }
+              { match: n => Element.isElement(n) && Editor.isBlock(editor, n) }
             )
           }
         }}