diff --git a/packages/vue-i18n-core/src/composer.ts b/packages/vue-i18n-core/src/composer.ts
index 7c8a3e67c..7a71f66bc 100644
--- a/packages/vue-i18n-core/src/composer.ts
+++ b/packages/vue-i18n-core/src/composer.ts
@@ -118,6 +118,8 @@ import { isLegacyVueI18n } from './utils'
 
 export { DEFAULT_LOCALE } from '@intlify/core-base'
 
+type LocalMessageKey=string
+
 // extend VNode interface
 export const DEVTOOLS_META = '__INTLIFY_META__'