diff --git a/psalm.xml b/psalm.xml
index cf33380..b099f1b 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -28,6 +28,7 @@
       </errorLevel>
     </MissingConstructor>
     <PropertyNotSetInConstructor errorLevel="suppress" />
+    <ImplementedReturnTypeMismatch errorLevel="suppress" />
   </issueHandlers>
 
   <mockClasses>
diff --git a/src/CreditCard.php b/src/CreditCard.php
index ccf905b..5552d37 100644
--- a/src/CreditCard.php
+++ b/src/CreditCard.php
@@ -10,7 +10,6 @@ class CreditCard extends \Omnipay\Common\CreditCard
     /**
      * Gets the card brand. Returns the brand that was set if one was set,
      * otherwise determines the brand from the card number.
-     *
      * @return string|null
      */
     public function getBrand()
diff --git a/src/ExtendedGateway.php b/src/ExtendedGateway.php
index a3da322..25006ee 100644
--- a/src/ExtendedGateway.php
+++ b/src/ExtendedGateway.php
@@ -77,13 +77,13 @@ public function fetchSubscription(array $parameters = array())
      * parameters passed.
      *
      * @param array $parameters
-     * @return \Omnipay\BlueSnap\Message\AbstractRequest
+     * @return \Omnipay\BlueSnap\Message\FetchSubscriptionsRequest
      */
     public function fetchSubscriptions(array $parameters = array())
     {
         if (isset($parameters['customerReference'])) {
             /**
-             * @var \Omnipay\BlueSnap\Message\AbstractRequest
+             * @var \Omnipay\BlueSnap\Message\FetchSubscriptionsRequest
              */
             return $this->createRequest(
                 '\Omnipay\BlueSnap\Message\ExtendedFetchSubscriptionsRequest',
diff --git a/src/Message/Response.php b/src/Message/Response.php
index 993ff68..76f7cf8 100644
--- a/src/Message/Response.php
+++ b/src/Message/Response.php
@@ -106,8 +106,9 @@ public function getMessage()
             if ($this->data instanceof SimpleXMLElement && isset($this->data->message->description)) {
                 return (string) $this->data->message->description;
             }
-            // some error responses are plain text instead of XML
-            return (string) $this->data;
+            if (is_string($this->data)) {
+                return $this->data;
+            }  // some error responses are plain text instead of XML
         }
 
         return null;
@@ -391,7 +392,7 @@ public function getNextChargeDate()
      */
     public function getTransactions()
     {
-        if (!isset($this->data['data'])) {
+        if (!is_array($this->data) || !isset($this->data['data'])) {
             return null;
         }
         $transactions = array();
diff --git a/tests/Framework/DataFaker.php b/tests/Framework/DataFaker.php
index df19966..65f8795 100644
--- a/tests/Framework/DataFaker.php
+++ b/tests/Framework/DataFaker.php
@@ -282,7 +282,7 @@ public function password()
     public function customerReference()
     {
         do {
-            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(6, 10));
+            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(6, 9));
         } while ($result == 0);
         return $result;
     }
@@ -295,7 +295,7 @@ public function customerReference()
     public function transactionReference()
     {
         do {
-            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(6, 10));
+            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(6, 9));
         } while ($result == 0);
         return $result;
     }
@@ -308,7 +308,7 @@ public function transactionReference()
     public function subscriptionReference()
     {
         do {
-            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(6, 10));
+            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(6, 9));
         } while ($result == 0);
         return $result;
     }
@@ -321,7 +321,7 @@ public function subscriptionReference()
     public function subscriptionChargeReference()
     {
         do {
-            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(3, 10));
+            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(3, 9));
         } while ($result == 0);
         return $result;
     }
@@ -347,7 +347,7 @@ public function storeReference()
     public function planReference()
     {
         do {
-            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(6, 10));
+            $result = $this->randomCharacters(self::DIGITS, $this->intBetween(6, 9));
         } while ($result == 0);
         return $result;
     }
diff --git a/tests/Framework/TestCase.php b/tests/Framework/TestCase.php
index dc395c3..d02f9ad 100644
--- a/tests/Framework/TestCase.php
+++ b/tests/Framework/TestCase.php
@@ -85,7 +85,7 @@ public function getMockHttpResponse($path, $substitutions = array())
      * then the function will replace all instances of '[NAME]' in the
      * response with 'Fake Name'. Substitutions are not required.
      *
-     * @param array<string>|string $paths
+     * @param array<string, string>|string $paths
      * @param array<string, string> $substitutions
      *
      * @return MockPlugin
@@ -95,8 +95,12 @@ public function setMockHttpResponse($paths, $substitutions = array())
         $this->substitutableMockHttpRequests = array();
         $that = $this;
         $mock = new MockPlugin(null, true);
-        $this->getHttpClient()->getEventDispatcher()->removeSubscriber($mock);
-        $mock->getEventDispatcher()->addListener(
+        /** @var \Symfony\Component\EventDispatcher\EventDispatcher */
+        $event_dispatcher = $this->getHttpClient()->getEventDispatcher();
+        $event_dispatcher->removeSubscriber($mock);
+        /** @var \Symfony\Component\EventDispatcher\EventDispatcher */
+        $mock_event_dispatcher = $mock->getEventDispatcher();
+        $mock_event_dispatcher->addListener(
             'mock.request',
             // @codingStandardsIgnoreStart
             /**
@@ -120,7 +124,7 @@ function (Event $event) use ($that) {
             $mock->addResponse($this->getMockHttpResponse($path, $substitutions) ?: '');
         }
 
-        $this->getHttpClient()->getEventDispatcher()->addSubscriber($mock);
+        $event_dispatcher->addSubscriber($mock);
 
         return $mock;
     }
diff --git a/tests/Message/ExtendedFetchSubscriptionsRequestTest.php b/tests/Message/ExtendedFetchSubscriptionsRequestTest.php
index f4cbd95..0777e30 100644
--- a/tests/Message/ExtendedFetchSubscriptionsRequestTest.php
+++ b/tests/Message/ExtendedFetchSubscriptionsRequestTest.php
@@ -116,7 +116,7 @@ public function testSendSuccess()
         $this->assertFalse($response->isRedirect());
         $this->assertSame('200', $response->getCode());
         $subscriptions = $response->getSubscriptions();
-        $this->assertSame(2, count($subscriptions));
+        $this->assertCount(2, $subscriptions);
         if ($subscriptions) {
             foreach ($subscriptions as $i => $subscription) {
                 $fakeSubscription = $fakeSubscriptions[intval($i) + 1];
diff --git a/tests/Message/ExtendedFetchTransactionRequestTest.php b/tests/Message/ExtendedFetchTransactionRequestTest.php
index a3bbd82..58b27cf 100644
--- a/tests/Message/ExtendedFetchTransactionRequestTest.php
+++ b/tests/Message/ExtendedFetchTransactionRequestTest.php
@@ -88,8 +88,8 @@ public function testSendSuccess()
         $fakeCard = $this->faker->card();
         $cardBrand = $fakeCard->getBrand();
         $cardLastFour = $fakeCard->getNumberLastFour();
-        $expiryMonth = $fakeCard->getExpiryMonth();
-        $expiryYear = $fakeCard->getExpiryYear();
+        $expiryMonth = (string) $fakeCard->getExpiryMonth();
+        $expiryYear = (string) $fakeCard->getExpiryYear();
         $firstName = $fakeCard->getFirstName();
         $lastName = $fakeCard->getLastName();
         $email = $fakeCard->getEmail();
@@ -152,8 +152,8 @@ public function testSendSuccess()
         }
         $this->assertSame($cardLastFour, $card->getNumberLastFour());
         $this->assertSame($cardBrand, $card->getBrand());
-        $this->assertSame($expiryMonth, $card->getExpiryMonth());
-        $this->assertSame($expiryYear, $card->getExpiryYear());
+        $this->assertSame($expiryMonth, (string) $card->getExpiryMonth());
+        $this->assertSame($expiryYear, (string) $card->getExpiryYear());
         $this->assertSame($firstName, $card->getFirstName());
         $this->assertSame($lastName, $card->getLastName());
         $this->assertSame($email, $card->getEmail());
diff --git a/tests/Message/FetchCanceledSubscriptionsRequestTest.php b/tests/Message/FetchCanceledSubscriptionsRequestTest.php
index 539fe32..58a76fe 100644
--- a/tests/Message/FetchCanceledSubscriptionsRequestTest.php
+++ b/tests/Message/FetchCanceledSubscriptionsRequestTest.php
@@ -201,7 +201,7 @@ public function testSendSuccess()
         $this->assertFalse($response->isRedirect());
         $this->assertSame('200', $response->getCode());
         $subscriptions = $response->getSubscriptions();
-        $this->assertSame(2, count($subscriptions));
+        $this->assertCount(2, $subscriptions);
         if ($subscriptions) {
             foreach ($subscriptions as $i => $subscription) {
                 $fakeSubscription = $fakeSubscriptions[intval($i) + 1];
diff --git a/tests/Message/FetchSubscriptionsRequestTest.php b/tests/Message/FetchSubscriptionsRequestTest.php
index 8bbf2d7..ce1c12a 100644
--- a/tests/Message/FetchSubscriptionsRequestTest.php
+++ b/tests/Message/FetchSubscriptionsRequestTest.php
@@ -158,7 +158,7 @@ public function testSendSuccess()
         $this->assertFalse($response->isRedirect());
         $this->assertSame('200', $response->getCode());
         $subscriptions = $response->getSubscriptions();
-        $this->assertSame(2, count($subscriptions));
+        $this->assertCount(2, $subscriptions);
         if ($subscriptions) {
             foreach ($subscriptions as $i => $subscription) {
                 $fakeSubscription = $fakeSubscriptions[intval($i) + 1];
diff --git a/tests/Message/FetchTransactionsRequestTest.php b/tests/Message/FetchTransactionsRequestTest.php
index 72aaed1..a374fe8 100644
--- a/tests/Message/FetchTransactionsRequestTest.php
+++ b/tests/Message/FetchTransactionsRequestTest.php
@@ -161,7 +161,7 @@ public function testSendSuccess()
         $this->assertFalse($response->isRedirect());
         $this->assertSame('200', $response->getCode());
         $transactions = $response->getTransactions();
-        $this->assertSame(2, count($transactions));
+        $this->assertCount(2, $transactions);
         if ($transactions) {
             foreach ($transactions as $i => $transaction) {
                 $fakeTransaction = $fakeTransactions[intval($i) + 1];