diff --git a/build.js b/build.js
index ca137e8..28a27eb 100644
--- a/build.js
+++ b/build.js
@@ -1,3 +1,4 @@
+"use strict";
 var stealTools = require("steal-tools");
 
 stealTools.export({
diff --git a/helpers/-make-delegate-event-tree.js b/helpers/-make-delegate-event-tree.js
index c4defc3..ea676d1 100644
--- a/helpers/-make-delegate-event-tree.js
+++ b/helpers/-make-delegate-event-tree.js
@@ -1,3 +1,4 @@
+"use strict";
 var KeyTree = require('can-key-tree');
 var canReflect = require('can-reflect');