diff --git a/lib/assert.js b/lib/assert.js
index 91144c2..abb3620 100644
--- a/lib/assert.js
+++ b/lib/assert.js
@@ -1,3 +1,5 @@
+'use strict';
+
 const assert = require('assert');
 const util = require('util');
 const fail = assert.fail;
diff --git a/package.json b/package.json
index eca11be..087b24b 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "description": "Core assert library extended slightly with few more assertion methods",
   "main": "lib/assert.js",
   "scripts": {
-    "test": "env NODE_ENV=test mocha --recursive --use_strict"
+    "test": "env NODE_ENV=test mocha --recursive"
   },
   "repository": {
     "type": "git",
diff --git a/test/assert.test.js b/test/assert.test.js
index 4d9f357..4de2a53 100644
--- a/test/assert.test.js
+++ b/test/assert.test.js
@@ -1,3 +1,5 @@
+'use strict';
+
 const assert = require('assert');
 const util = require('util');
 const assertExtended = require('../lib/assert');