diff --git a/src/Mailgun/Constants/Constants.php b/src/Mailgun/Constants/Constants.php
index 107db16..3165183 100644
--- a/src/Mailgun/Constants/Constants.php
+++ b/src/Mailgun/Constants/Constants.php
@@ -6,6 +6,7 @@ const SDK_USER_AGENT = "mailgun-sdk-php";
 const RECIPIENT_COUNT_LIMIT = 1000;
 const CAMPAIGN_ID_LIMIT = 3;
 const TAG_LIMIT = 3;
+const DEFAULT_TIME_ZONE = "UTC";
 
 //Common Exception Messages
 const EXCEPTION_INVALID_CREDENTIALS = "Your credentials are incorrect.";
diff --git a/tests/Mailgun/Tests/Messages/MessageBuilderTest.php b/tests/Mailgun/Tests/Messages/MessageBuilderTest.php
index 8f5a3df..f8e3a2f 100644
--- a/tests/Mailgun/Tests/Messages/MessageBuilderTest.php
+++ b/tests/Mailgun/Tests/Messages/MessageBuilderTest.php
@@ -153,6 +153,9 @@ class MessageBuilderTest extends \Mailgun\Tests\MailgunTestCase{
 		$message->setDeliveryTime("January 15, 2014 8:00AM", "UTC");
 		$messageObj = $message->getMessage();
 		$this->assertEquals(array("o:deliverytime" => "Wed, 15 Jan 2014 08:00:00 +0000"), $messageObj);
+		$message->setDeliveryTime("January 15, 2014 8:00AM");
+		$messageObj = $message->getMessage();
+		$this->assertEquals(array("o:deliverytime" => "Wed, 15 Jan 2014 08:00:00 +0000"), $messageObj);
 		$message->setDeliveryTime("1/15/2014 13:50:01", "CDT");
 		$messageObj = $message->getMessage();
 		$this->assertEquals(array("o:deliverytime" => "Wed, 15 Jan 2014 13:50:01 -0600"), $messageObj);