diff --git a/framework/captcha/CaptchaAction.php b/framework/captcha/CaptchaAction.php
index 439994ed11..93b1dcb604 100644
--- a/framework/captcha/CaptchaAction.php
+++ b/framework/captcha/CaptchaAction.php
@@ -184,7 +184,7 @@ class CaptchaAction extends Action
         $session = Yii::$app->getSession();
         $session->open();
         $name = $this->getSessionKey() . 'count';
-        ++$session[$name];
+        $session[$name] = $session[$name] + 1;
         if ($valid || $session[$name] > $this->testLimit && $this->testLimit > 0) {
             $this->getVerifyCode(true);
         }