diff --git a/index.js b/index.js
index 437971e..167a8f1 100644
--- a/index.js
+++ b/index.js
@@ -209,7 +209,7 @@ class ServerlessS3Sync {
       if (s.hasOwnProperty('acl')) {
         acl = s.acl;
       }
-      if (!s.bucketName || !s.localDir) {
+      if ((!s.bucketName && !s.bucketNameKey) || !s.localDir) {
         throw 'Invalid custom.s3Sync';
       }
       const localDir = path.join(servicePath, s.localDir);