diff --git a/tests/OrderCouponTest.php b/tests/OrderCouponTest.php
index c8a6df9..7af6881 100644
--- a/tests/OrderCouponTest.php
+++ b/tests/OrderCouponTest.php
@@ -73,7 +73,7 @@ public function testPercent()
         );
         $coupon->write();
         $context = ['CouponCode' => $coupon->Code];
-        $this->assertTrue($coupon->validateOrder($this->cart, $context), $coupon->getMessage());
+        $this->assertTrue($coupon->validateOrder($this->cart, $context), (string)$coupon->getMessage());
         $this->assertEquals(4, $coupon->getDiscountValue(10), '40% off value');
         $this->assertEquals(200, $this->calc($this->unpaid, $coupon), '40% off order');
     }
@@ -92,9 +92,9 @@ public function testAmount()
         $coupon->write();
 
         $context = ['CouponCode' => $coupon->Code];
-        $this->assertTrue($coupon->validateOrder($this->cart, $context), $coupon->getMessage());
+        $this->assertTrue($coupon->validateOrder($this->cart, $context), (string)$coupon->getMessage());
         $this->assertEquals($coupon->getDiscountValue(1000), 10, '$10 off fixed value');
-        $this->assertTrue($coupon->validateOrder($this->unpaid, $context), $coupon->getMessage());
+        $this->assertTrue($coupon->validateOrder($this->unpaid, $context), (string)$coupon->getMessage());
         $this->assertEquals(60, $this->calc($this->unpaid, $coupon), '$10 off each item: $60 total');
         //TODO: test amount that is greater than item value
     }