diff --git a/src/Mailgun/Messages/MessageBuilder.php b/src/Mailgun/Messages/MessageBuilder.php
index 34dd4da..a9139a5 100644
--- a/src/Mailgun/Messages/MessageBuilder.php
+++ b/src/Mailgun/Messages/MessageBuilder.php
@@ -117,10 +117,10 @@ class MessageBuilder
     {
         $compiledAddress = $this->parseAddress($address, $variables);
 
-        if (isset($this->message[$headerName])) {
-            array_push($this->message[$headerName], $compiledAddress);
-        } elseif ($headerName == 'h:reply-to') {
+        if ($headerName === 'h:reply-to') {
             $this->message[$headerName] = $compiledAddress;
+        } elseif (isset($this->message[$headerName])) {
+            array_push($this->message[$headerName], $compiledAddress);
         } else {
             $this->message[$headerName] = [$compiledAddress];
         }
diff --git a/tests/Messages/MessageBuilderTest.php b/tests/Messages/MessageBuilderTest.php
index 3c50fe3..70eb179 100644
--- a/tests/Messages/MessageBuilderTest.php
+++ b/tests/Messages/MessageBuilderTest.php
@@ -114,6 +114,7 @@ class MessageBuilderTest extends \Mailgun\Tests\MailgunTestCase
     public function testSetReplyTo()
     {
         $message = $this->client->MessageBuilder();
+        $message->setReplyToAddress('overwritten@samples.mailgun.org');
         $message->setReplyToAddress('test@samples.mailgun.org', ['first' => 'Test', 'last' => 'User']);
         $messageObj = $message->getMessage();
         $this->assertEquals(['h:reply-to' => "'Test User' <test@samples.mailgun.org>"], $messageObj);