diff --git a/README-English.md b/README-English.md
index 0ac319d1..75858307 100644
--- a/README-English.md
+++ b/README-English.md
@@ -85,7 +85,7 @@ git clone https://github.com/Yamato-Security/hayabusa.git
 You can get latest Hayabusa rules with the execute following command.
 
 ```bash
-.\hayabusa.exe -U
+.\hayabusa.exe -u
 ```
 
 If you forget to use `--recursive` option, `rules/` files which managed in submodule did not cloned.
diff --git a/README-Japanese.md b/README-Japanese.md
index 9291a5c0..2de43e84 100644
--- a/README-Japanese.md
+++ b/README-Japanese.md
@@ -86,7 +86,7 @@ git clone https://github.com/Yamato-Security/hayabusa.git
 Hayabusaでは検知ルールを`rules/`フォルダの取得はコンパイル後に以下のコマンドでルールの最新版を取得することができます。
 
 ```bash
-.\hayabusa.exe -U
+.\hayabusa.exe -u
 ```
 
 # ソースコードからのコンパイル（任意）