diff --git a/src/applications/files/engine/PhabricatorS3FileStorageEngine.php b/src/applications/files/engine/PhabricatorS3FileStorageEngine.php
--- a/src/applications/files/engine/PhabricatorS3FileStorageEngine.php
+++ b/src/applications/files/engine/PhabricatorS3FileStorageEngine.php
@@ -21,7 +21,8 @@
   }
 
   public function shouldBeEnabled($data, array $params) {
-    return (bool)PhabricatorEnv::getEnvConfig('storage.s3.bucket');
+    return PhabricatorEnv::getEnvConfig('storage.s3.bucket') &&
+      PhabricatorEnv::getEnvConfig('amazon-s3.access-key');
   }