diff --git a/benchmark/compiling.js b/benchmark/compiling.js
index 537415e..7638727 100644
--- a/benchmark/compiling.js
+++ b/benchmark/compiling.js
@@ -1,3 +1,5 @@
+'use strict'
+
 /**
  * Globals for benchmark.js
  */
diff --git a/benchmark/index.js b/benchmark/index.js
index 325a305..4b5af22 100644
--- a/benchmark/index.js
+++ b/benchmark/index.js
@@ -1,3 +1,5 @@
+'use strict'
+
 const fs = require('node:fs')
 const path = require('node:path')
 const spawn = require('node:child_process').spawn
diff --git a/benchmark/kind.js b/benchmark/kind.js
index 50081f5..239ccf9 100644
--- a/benchmark/kind.js
+++ b/benchmark/kind.js
@@ -1,3 +1,5 @@
+'use strict'
+
 /**
  * Globals for benchmark.js
  */
diff --git a/benchmark/matching.js b/benchmark/matching.js
index 2bcfabb..d584c68 100644
--- a/benchmark/matching.js
+++ b/benchmark/matching.js
@@ -1,3 +1,5 @@
+'use strict'
+
 /**
  * Globals for benchmark.js
  */