diff --git a/appengine/standard/mailgun/app.php b/appengine/standard/mailgun/app.php
index c06d32860f..dd81169340 100644
--- a/appengine/standard/mailgun/app.php
+++ b/appengine/standard/mailgun/app.php
@@ -20,7 +20,7 @@
 $app = new Application();
 
 $app->get('/', function () use ($app) {
-    if ($app['mailgun.domain'] == 'MAILGUN_DOMAIN_NAME') {
+    if ($app['mailgun.domain'] == 'MAILGUN_DOMAIN') {
         return 'set your mailgun domain and API key in <code>index.php</code>';
     }
 
diff --git a/appengine/standard/mailgun/index.php b/appengine/standard/mailgun/index.php
index 6997c26ed8..7e2b8af0ea 100644
--- a/appengine/standard/mailgun/index.php
+++ b/appengine/standard/mailgun/index.php
@@ -22,7 +22,7 @@
 $app = require __DIR__ . '/app.php';
 
 // set your Mailgun domain name and API key
-$app['mailgun.domain'] = 'MAILGUN_DOMAIN_NAME';
+$app['mailgun.domain'] = 'MAILGUN_DOMAIN';
 $app['mailgun.api_key'] = 'MAILGUN_APIKEY';
 
 // Run the app!
diff --git a/appengine/standard/mailgun/test/DeployAppEngineFlexTest.php b/appengine/standard/mailgun/test/DeployAppEngineFlexTest.php
index f0dc51d1d1..df8a5a9ddc 100644
--- a/appengine/standard/mailgun/test/DeployAppEngineFlexTest.php
+++ b/appengine/standard/mailgun/test/DeployAppEngineFlexTest.php
@@ -23,21 +23,29 @@ class DeployAppEngineFlexTest extends \PHPUnit_Framework_TestCase
 {
     use AppEngineDeploymentTrait;
 
-    public function beforeDeploy()
+    public static function beforeDeploy()
     {
+        // set your Mailgun domain name and API key
+        $mailgunDomain = getenv('MAILGUN_DOMAIN');
+        $mailgunApiKey = getenv('MAILGUN_APIKEY');
+
+        if (empty($mailgunDomain) || empty($mailgunApiKey)) {
+            self::markTestSkipped('set the MAILGUN_DOMAIN and MAILGUN_APIKEY environment variables');
+        }
+
         $tmpDir = FileUtil::cloneDirectoryIntoTmp(__DIR__ . '/..');
         FileUtil::copyDir(__DIR__ . '/../../../flexible/mailgun', $tmpDir);
         self::$gcloudWrapper->setDir($tmpDir);
         chdir($tmpDir);
         $indexPhp = file_get_contents('index.php');
         $indexPhp = str_replace(
-            'MAILGUN_DOMAIN_NAME',
-            getenv('MAILGUN_DOMAIN_NAME'),
+            'MAILGUN_DOMAIN',
+            $mailgunDomain,
             $indexPhp
         );
         $indexPhp = str_replace(
             'MAILGUN_APIKEY',
-            getenv('MAILGUN_APIKEY'),
+            $mailgunApiKey,
             $indexPhp
         );
         file_put_contents('index.php', $indexPhp);