diff --git a/lambda/src/index.ts b/lambda/src/index.ts
index 69aa50a..3609840 100644
--- a/lambda/src/index.ts
+++ b/lambda/src/index.ts
@@ -180,7 +180,7 @@ let BROWSER: Promise<Browser>|null = null;
 
 async function doRender(file: string, path: string, src: string, out: string) {
   const [ kind, handout, part ] = `${path}/${file.replace(/(index)?\.s?html/, '')}`.split('/');
-  const deliver = `?handout-deliver=${kind}/${handout}/${part || ''}/`;
+  const deliver = `?handout-deliver=${kind}/${handout || 'index'}/${part || ''}/`;
   if ( ! BROWSER) {
     BROWSER = Chromium.executablePath.then(executablePath => Chromium.puppeteer.launch({
       args: Chromium.args,