diff --git a/.travis.yml b/.travis.yml
index 651e42b..aafa6e4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,6 +9,7 @@ php:
 # This triggers builds to run on the new TravisCI infrastructure.
 # See: http://docs.travis-ci.com/user/workers/container-based-infrastructure/
 sudo: false
+
 ## Cache composer
 cache:
   directories:
diff --git a/src/Traits/HasGatewayParams.php b/src/Traits/HasGatewayParams.php
index 8b32b5e..c06753a 100644
--- a/src/Traits/HasGatewayParams.php
+++ b/src/Traits/HasGatewayParams.php
@@ -8,6 +8,7 @@
  */
 
 use Omnipay\Payone\AbstractShopGateway;
+use Omnipay\Common\Exception\InvalidRequestException;
 
 trait HasGatewayParams
 {
diff --git a/tests/ShopServerGatewayTest.php b/tests/ShopServerGatewayTest.php
index d9cb978..3be7181 100644
--- a/tests/ShopServerGatewayTest.php
+++ b/tests/ShopServerGatewayTest.php
@@ -3,6 +3,7 @@
 namespace Omnipay\Payone;
 
 use Omnipay\Tests\GatewayTestCase;
+//use Omnipay\Common\Exception\InvalidRequestException;
 
 class ShopServerGatewayTest extends GatewayTestCase
 {
@@ -220,4 +221,15 @@ public function testPurchaseFailure()
         $this->assertSame('Invalid card expiry date. Please verify your card data.', $response->getCustomerMessage());
         $this->assertNull($response->getTransactionReference());
     }
+
+    /**
+     * See https://github.com/academe/OmniPay-Payone/issues/31
+     * @expectedException Omnipay\Common\Exception\InvalidRequestException
+     */
+    public function testInvalidMerchantId()
+    {
+        $this->gateway->initialize([
+            'merchantId' => 'abcdef',
+        ]);
+    }
 }