diff --git a/src/node/markdown/markdown.ts b/src/node/markdown/markdown.ts
index a091639a..be4b8250 100644
--- a/src/node/markdown/markdown.ts
+++ b/src/node/markdown/markdown.ts
@@ -113,6 +113,7 @@ export interface MarkdownOptions extends Options {
   /**
    * Custom language labels for display.
    * Overrides the default language label shown in code blocks.
+   * Keys are case-insensitive.
    *
    * @example { 'vue': 'Vue SFC' }
    */
diff --git a/src/node/markdown/plugins/highlight.ts b/src/node/markdown/plugins/highlight.ts
index 780e37e8..8a3dd9e0 100644
--- a/src/node/markdown/plugins/highlight.ts
+++ b/src/node/markdown/plugins/highlight.ts
@@ -68,14 +68,12 @@ export async function highlight(
       ...(options.languages || []),
       ...Object.values(options.languageAlias || {})
     ],
-    langAlias: options.languageAlias
-      ? Object.fromEntries(
-          Object.entries(options.languageAlias).map(([key, value]) => [
-            key.toLowerCase(),
-            value
-          ])
-        )
-      : undefined
+    langAlias: Object.fromEntries(
+      Object.entries(options.languageAlias || {}).map(([k, v]) => [
+        k.toLowerCase(),
+        v
+      ])
+    )
   })
 
   await options?.shikiSetup?.(highlighter)
diff --git a/src/node/markdown/plugins/preWrapper.ts b/src/node/markdown/plugins/preWrapper.ts
index 38266509..c357c1d6 100644
--- a/src/node/markdown/plugins/preWrapper.ts
+++ b/src/node/markdown/plugins/preWrapper.ts
@@ -6,6 +6,13 @@ export interface Options {
 }
 
 export function preWrapperPlugin(md: MarkdownItAsync, options: Options) {
+  const languageLabel = Object.fromEntries(
+    Object.entries(options.languageLabel || {}).map(([k, v]) => [
+      k.toLowerCase(),
+      v
+    ])
+  )
+
   const fence = md.renderer.rules.fence!
   md.renderer.rules.fence = (...args) => {
     const [tokens, idx] = args
@@ -18,7 +25,8 @@ export function preWrapperPlugin(md: MarkdownItAsync, options: Options) {
     token.info = token.info.replace(/ active$/, '').replace(/ active /, ' ')
 
     const lang = extractLang(token.info)
-    const langLabel = options.languageLabel?.[lang] || lang.replace(/_/g, ' ')
+    const langLabel =
+      languageLabel[lang.toLowerCase()] || lang.replace(/_/g, ' ')
 
     return (
       `<div class="language-${lang}${active}">` +