diff --git a/.travis.yml b/.travis.yml
index 69660bd..8572747 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,6 +4,7 @@ language: node_js
 
 matrix:
   include:
+    - node_js: "4"
     - node_js: "6"
     - node_js: "7"
       env: COVERALLS=1
diff --git a/lib/index.js b/lib/index.js
index 34a4f1a..0a17599 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -16,7 +16,8 @@ const handlers = require('./handlers');
  * @param {Boolean} [options.scope] - If true all nodes will be elements of root block.
  * @returns {Function} transform function
  */
-function transformFactory(tree, options = {}) {
+function transformFactory(tree, options) {
+    options || (options = {});
 
     transform.definition = definitions(tree, options);
     transform.handlers = Object.assign({}, handlers);
diff --git a/package.json b/package.json
index 4e7cebc..8e3b7b2 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,7 @@
     "github-release": "conventional-github-releaser -p angular -r 0"
   },
   "engines": {
-    "node": ">= 6"
+    "node": ">= 4"
   },
   "repository": {
     "type": "git",