diff --git a/server/middleware/20.cidx.ts b/server/middleware/20.cidx.ts
new file mode 100644
index 0000000..60d2b44
--- /dev/null
+++ b/server/middleware/20.cidx.ts
@@ -0,0 +1,4 @@
+export default eventHandler((ev) => {
+	let chapParam = getRouterParams(ev).chapter;
+	ev.context.chapterIndex = !!chapParam ? parseInt(chapParam) - 1 : 0;
+});