diff --git a/app/Libs/WxMicroPay.class.php b/app/Libs/WxMicroPay.class.php
index 1072141..289e52c 100644
--- a/app/Libs/WxMicroPay.class.php
+++ b/app/Libs/WxMicroPay.class.php
@@ -33,7 +33,7 @@ class WxMicroPay extends WxPayCommon
                 throw new Exception("缺少必填参数total_fee！");
             } elseif (!$this->parameters["auth_code"]) {
                 throw new Exception("缺少必填参数auth_code！");
-            } elseif (strlen($this->parameters["auth_code"]) != 18) {
+            } elseif (strlen((string)$this->parameters["auth_code"]) != 18) {
                 throw new Exception("支付码不正确！");
             }