diff --git a/src/template.tsx b/src/template.tsx
index 19a5ea1..c8de9c9 100644
--- a/src/template.tsx
+++ b/src/template.tsx
@@ -4,6 +4,8 @@ import { render } from 'jsx-email'
 import Turndown from 'turndown'
 import type { JSX } from 'preact'
 
+console.assert(React !== undefined)
+
 const htmlToMd = new Turndown({
 	headingStyle: 'atx',
 	codeBlockStyle: 'fenced',