diff --git a/src/node/utils/promises.js b/src/node/utils/promises.js
index 60c1cff2a..0c8dc24f3 100644
--- a/src/node/utils/promises.js
+++ b/src/node/utils/promises.js
@@ -1,3 +1,4 @@
+'use strict';
 /**
  * Helpers to manipulate promises (like async but for promises).
  */