diff --git a/lib/mdx.tsx b/lib/mdx.tsx
index 9f782f0d2..0996a3440 100644
--- a/lib/mdx.tsx
+++ b/lib/mdx.tsx
@@ -157,7 +157,7 @@ export const useCurrentTocIndex: (
       }
     }
     if (active != null) {
-      const nextHeading = _headings[_headings.indexOf(active as Heading) + 1]
+      const nextHeading = _headings[_headings.indexOf(active) + 1]
       const nextHeadingNode = document.getElementById(
         nextHeading?.link.slice(1) ?? ''
       )
@@ -166,9 +166,7 @@ export const useCurrentTocIndex: (
         nextHeadingNode.offsetTop - navHeight <
           document.documentElement.scrollTop + window.innerHeight
       setCurrentIndex(
-        (isNextHeadingInView
-          ? (nextHeading?.link ?? '')
-          : (active?.link ?? '')) as string
+        isNextHeadingInView ? (nextHeading?.link ?? '') : (active?.link ?? '')
       )
     } else setCurrentIndex(_headings[0]?.children?.[0]?.link ?? '')
   }, [headings, navHeight])