diff --git a/src/node/markdown/markdown.ts b/src/node/markdown/markdown.ts
index 513c5c0e..c549901d 100644
--- a/src/node/markdown/markdown.ts
+++ b/src/node/markdown/markdown.ts
@@ -107,7 +107,7 @@ export interface MarkdownOptions extends MarkdownIt.Options {
   /**
    * Setup Shikiji instance
    */
-  shikijiSetup?: (shikiji: Highlighter) => Promise<void>
+  shikijiSetup?: (shikiji: Highlighter) => void | Promise<void>
 
   /* ==================== Markdown It Plugins ==================== */