diff --git a/lib/render/engineScript.js b/lib/render/engineScript.js
index 56aa472..c2f31bd 100644
--- a/lib/render/engineScript.js
+++ b/lib/render/engineScript.js
@@ -36,7 +36,7 @@ module.exports = function (inputs, callback, done) {
 
   let isFromCache = true
 
-  let engine = (template) => {
+  const engine = (template) => {
     const key = template + ':' + inputs.engine
 
     if (!compiledCache.get(key)) {
@@ -56,9 +56,6 @@ module.exports = function (inputs, callback, done) {
     inputs.parentModuleDirectory
   ]
 
-  let consoleFromSandbox
-  let consoleMessages = []
-
   function respondWrap (rawErr, content) {
     let err
 
@@ -146,8 +143,8 @@ module.exports = function (inputs, callback, done) {
     }
   )
 
-  consoleMessages = messages
-  consoleFromSandbox = consoleSandbox
+  const consoleMessages = messages
+  const consoleFromSandbox = consoleSandbox
 
   let templateHelpers = inputs.template.helpers
   let originalTemplateHelpersStr
@@ -166,7 +163,7 @@ module.exports = function (inputs, callback, done) {
 
         templateHelpers = {}
 
-        for (let fn in sandboxContext) {
+        for (const fn in sandboxContext) {
           if (typeof sandboxContext[fn] === 'function') {
             templateHelpers[fn] = sandboxContext[fn]
           }
diff --git a/lib/render/safeSandbox.js b/lib/render/safeSandbox.js
index 857ae6f..2cd27e5 100644
--- a/lib/render/safeSandbox.js
+++ b/lib/render/safeSandbox.js
@@ -111,7 +111,7 @@ module.exports = (_sandbox, options = {}) => {
     return result
   }
 
-  for (let name in sandbox) {
+  for (const name in sandbox) {
     vm._internal.Contextify.globalValue(sandbox[name], name)
   }
 
diff --git a/lib/store/collection.js b/lib/store/collection.js
index eb20368..949dc4a 100644
--- a/lib/store/collection.js
+++ b/lib/store/collection.js
@@ -143,7 +143,7 @@ module.exports = (entitySet, provider, model) => ({
     return docs.map((doc) => {
       const newDoc = Object.assign({}, doc)
 
-      for (let prop in newDoc) {
+      for (const prop in newDoc) {
         if (!prop) {
           continue
         }
@@ -170,7 +170,7 @@ module.exports = (entitySet, provider, model) => ({
     return docs.map((doc) => {
       const newDoc = Object.assign({}, doc)
 
-      for (let prop in newDoc) {
+      for (const prop in newDoc) {
         if (!prop) {
           continue
         }
diff --git a/lib/store/documentStore.js b/lib/store/documentStore.js
index 6ab98b4..a688861 100644
--- a/lib/store/documentStore.js
+++ b/lib/store/documentStore.js
@@ -237,7 +237,7 @@ function typeDefToJSONSchema (model, def) {
     const propDef = def[key]
     const collectionTypeRegExp = /^Collection\((\S+)\)$/
     let type = propDef.type
-    let extraSchema = propDef.schema
+    const extraSchema = propDef.schema
     let isCollection = false
 
     if (propDef == null || type == null) {
diff --git a/test/render/engineTest.js b/test/render/engineTest.js
index 377f58b..3d41090 100644
--- a/test/render/engineTest.js
+++ b/test/render/engineTest.js
@@ -6,7 +6,7 @@ const safeSandboxPath = path.join(__dirname, '../../lib/render/safeSandbox')
 
 describe('engine', () => {
   describe('engine with dedicated-process strategy', () => {
-    let scriptManager = ScriptManager({ strategy: 'dedicated-process' })
+    const scriptManager = ScriptManager({ strategy: 'dedicated-process' })
 
     beforeEach((done) => {
       scriptManager.ensureStarted(done)
@@ -17,7 +17,7 @@ describe('engine', () => {
   })
 
   describe('engine with http-server strategy', () => {
-    let scriptManager = ScriptManager({ strategy: 'http-server' })
+    const scriptManager = ScriptManager({ strategy: 'http-server' })
 
     beforeEach((done) => {
       scriptManager.ensureStarted(done)
@@ -29,7 +29,7 @@ describe('engine', () => {
   })
 
   describe('engine with in-process strategy', function () {
-    let scriptManager = ScriptManager({ strategy: 'in-process' })
+    const scriptManager = ScriptManager({ strategy: 'in-process' })
 
     beforeEach((done) => {
       scriptManager.ensureStarted(done)
diff --git a/test/reporterTest.js b/test/reporterTest.js
index f890911..a9125cc 100644
--- a/test/reporterTest.js
+++ b/test/reporterTest.js
@@ -76,7 +76,7 @@ describe('reporter', () => {
       }
     })
     stdMocks.restore()
-    let stdoutContent = stdMocks.flush()
+    const stdoutContent = stdMocks.flush()
     stdoutContent.stdout.length.should.be.eql(0)
 
     const allTransportsAreSilent = Object.keys(reporter.logger.transports).every(function (transportName) {