diff --git a/src/Message/CancelSubscriptionRequest.php b/src/Message/CancelSubscriptionRequest.php
index 30de0819..beb362e2 100644
--- a/src/Message/CancelSubscriptionRequest.php
+++ b/src/Message/CancelSubscriptionRequest.php
@@ -61,9 +61,14 @@ public function getData()
     {
         $this->validate('customerReference', 'subscriptionReference');
 
-        $data = array(
-            'at_period_end' => $this->getAtPeriodEnd()
-        );
+        $data = array();
+
+        // NOTE: Boolean must be passed as string
+        // Otherwise it will be converted as numeric 1 or 2
+        // Causing an error with the API
+        if ($this->getAtPeriodEnd()) {
+            $data['at_period_end'] = 'true';
+        }
 
         return $data;
     }
diff --git a/tests/Message/CancelSubscriptionRequestTest.php b/tests/Message/CancelSubscriptionRequestTest.php
index 6d5f047e..015197f4 100644
--- a/tests/Message/CancelSubscriptionRequestTest.php
+++ b/tests/Message/CancelSubscriptionRequestTest.php
@@ -11,11 +11,16 @@ public function setUp()
         $this->request = new CancelSubscriptionRequest($this->getHttpClient(), $this->getHttpRequest());
         $this->request->setCustomerReference('cus_7lfqk3Om3t4xSU');
         $this->request->setSubscriptionReference('sub_7mU0FokE8GQZFW');
+        $this->request->setAtPeriodEnd(true);
     }
 
     public function testEndpoint()
     {
         $this->assertSame('https://api.stripe.com/v1/customers/cus_7lfqk3Om3t4xSU/subscriptions/sub_7mU0FokE8GQZFW', $this->request->getEndpoint());
+        $this->assertSame(true, $this->request->getAtPeriodEnd());
+
+        $data = $this->request->getData();
+        $this->assertSame('true', $data['at_period_end']);
     }
 
     public function testSendSuccess()