diff --git a/index.js b/index.js
index c5b0c469..965a1806 100644
--- a/index.js
+++ b/index.js
@@ -1 +1,3 @@
+'use strict'
+
 module.exports = require('./lib/tedious')
diff --git a/lib/datatypes.js b/lib/datatypes.js
index ce2ce6f3..583eda75 100644
--- a/lib/datatypes.js
+++ b/lib/datatypes.js
@@ -1,4 +1,5 @@
 'use strict'
+
 const objectHasProperty = require('./utils').objectHasProperty
 const inspect = Symbol.for('nodejs.util.inspect.custom')
 
diff --git a/lib/utils.js b/lib/utils.js
index 9261c3fa..2ee8b2d2 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -1,3 +1,5 @@
+'use strict'
+
 const IDS = new WeakMap()
 const INCREMENT = {
   Connection: 1,
diff --git a/msnodesqlv8.js b/msnodesqlv8.js
index 0b67bbdb..632b5a5b 100644
--- a/msnodesqlv8.js
+++ b/msnodesqlv8.js
@@ -1 +1,3 @@
+'use strict'
+
 module.exports = require('./lib/msnodesqlv8')
diff --git a/tedious.js b/tedious.js
index c5b0c469..965a1806 100644
--- a/tedious.js
+++ b/tedious.js
@@ -1 +1,3 @@
+'use strict'
+
 module.exports = require('./lib/tedious')