diff --git a/specification/_types/analysis/kuromoji-plugin.ts b/specification/_types/analysis/kuromoji-plugin.ts
index b3caf986d2..d387d5c2c3 100644
--- a/specification/_types/analysis/kuromoji-plugin.ts
+++ b/specification/_types/analysis/kuromoji-plugin.ts
@@ -25,7 +25,7 @@ import { TokenizerBase } from './tokenizers'
 
 export class KuromojiAnalyzer {
   type: 'kuromoji'
-  mode: KuromojiTokenizationMode
+  mode?: KuromojiTokenizationMode
   user_dictionary?: string
 }