diff --git a/src/Client.php b/src/Client.php
index 11e755bb..3d65563c 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -386,9 +386,12 @@ public function refreshToken($token = null)
 
 		$response = $this->http->post($this->getOption('tokenurl'), $data);
 
+		// Make sure all headers are lowercase
+		$response->headers = array_change_key_case($response->headers, CASE_LOWER);
+
 		if ($response->code >= 200 || $response->code < 400)
 		{
-			if (strpos($response->headers['Content-Type'], 'application/json') !== false)
+			if (strpos($response->headers['content-type'], 'application/json') !== false)
 			{
 				$token = array_merge(json_decode($response->body, true), array('created' => time()));
 			}