diff --git a/components/mdx.tsx b/components/mdx.tsx
index c34a42d..f86ff6b 100644
--- a/components/mdx.tsx
+++ b/components/mdx.tsx
@@ -7,6 +7,9 @@ export function S<E extends React.ElementType='span'>({
   $?: string,
   _?: string,
 } & React.ComponentProps<E>) {
-  const cls = [className, ...(modifier.match(/\.(\w+)/g) ?? [])].map(s => s.slice(1)).join(' ');
+  const cls = [
+    ...(className ? [className] : []),
+    ...(modifier.match(/\.(\w+)/g) ?? []),
+  ].map(s => s.slice(1)).join(' ');
   return <TagName className={cls} {...props}>{children}</TagName>;
 }