diff --git a/tasks/build-ext.js b/tasks/build-ext.js
index 2357e431e8..211e5df494 100644
--- a/tasks/build-ext.js
+++ b/tasks/build-ext.js
@@ -1,3 +1,5 @@
+'use strict';
+
 const cleanup = require('rollup-plugin-cleanup');
 const common = require('rollup-plugin-commonjs');
 const node = require('rollup-plugin-node-resolve');