diff --git a/ticc.js b/ticc.js
index 8169381..27aad3a 100644
--- a/ticc.js
+++ b/ticc.js
@@ -968,7 +968,7 @@ class TicCrypto {
    */
   static randomize_number ({ length, min, max } = {}) {
     // 长度为 length 的随机数字，或者 (min||0) <= num < max
-    var num = 0
+    let num = 0
     if (typeof length === 'number' && length > 0) {
       num = parseInt(Math.random() * Math.pow(10, length))
       num = this.padStart(num.toString(), length, '0')