diff --git a/app/code/core/Mage/SalesRule/Model/Rule.php b/app/code/core/Mage/SalesRule/Model/Rule.php
index 9325bd7d885..2055367d69b 100644
--- a/app/code/core/Mage/SalesRule/Model/Rule.php
+++ b/app/code/core/Mage/SalesRule/Model/Rule.php
@@ -200,7 +200,7 @@ protected function _afterLoad()
      */
     protected function _afterSave()
     {
-        $couponCode = trim($this->getCouponCode());
+        $couponCode = trim((string)$this->getCouponCode());
         if (strlen($couponCode)
             && $this->getCouponType() == self::COUPON_TYPE_SPECIFIC
             && !$this->getUseAutoGeneration()