diff --git a/src/core.js b/src/core.js
index 325f9f02..82d3d684 100644
--- a/src/core.js
+++ b/src/core.js
@@ -62,7 +62,7 @@ function callPenthouse(document, options) {
   }
 
   if (user && pass) {
-    config.customPageHeaders = {...customPageHeaders, Authorization: 'Basic ' + token(user, pass)};
+    config.customPageHeaders = {...customPageHeaders, Authorization: `Basic ${token(user, pass)}`};
   }
 
   return sizes.map(({width, height}) => () => {
@@ -211,7 +211,7 @@ async function create(options = {}) {
       const uncriticalHref = normalizePath(path.relative(document.cwd, path.resolve(base, target.uncritical)));
       // Only replace stylesheets if the uncriticalHref is inside document.cwd and replaceStylesheets is not set via options
       if (!/^\.\.\//.test(uncriticalHref) && replaceStylesheets === undefined) {
-        inline.replaceStylesheets = ['/' + uncriticalHref];
+        inline.replaceStylesheets = [`/${uncriticalHref}`];
       }
     } else {
       inline.extract = extract;
diff --git a/src/file.js b/src/file.js
index 1cdcb08a..c8b306ef 100644
--- a/src/file.js
+++ b/src/file.js
@@ -306,7 +306,7 @@ async function fetch(uri, options = {}, secure = true) {
 
   request.rejectUnauthorized = false;
   if (user && pass) {
-    headers.Authorization = 'Basic ' + token(user, pass);
+    headers.Authorization = `Basic ${token(user, pass)}`;
   }
 
   if (userAgent) {
diff --git a/test/blackbox.test.js b/test/blackbox.test.js
index 50e57105..ba3da521 100644
--- a/test/blackbox.test.js
+++ b/test/blackbox.test.js
@@ -16,7 +16,7 @@ jest.setTimeout(60000);
 process.chdir(path.resolve(__dirname));
 
 function assertCritical(target, expected, done, skipTarget) {
-  return function(err, {css, html} = {}) {
+  return (err, {css, html} = {}) => {
     const output = /\.css$/.test(target) ? css : html;
 
     if (err) {
diff --git a/test/file.test.js b/test/file.test.js
index c167559a..f9c8201e 100644
--- a/test/file.test.js
+++ b/test/file.test.js
@@ -359,7 +359,7 @@ test('Get document from source with rebase option', async () => {
   // expect.assertions(tests.length + 1);
   for (const testdata of tests) {
     const {filepath, expected} = testdata;
-    const rebase = {to: '/' + normalizePath(path.relative(base, filepath))};
+    const rebase = {to: `/${normalizePath(path.relative(base, filepath))}`};
     const source = await fs.readFile(filepath);
     const file = await getDocumentFromSource(source, {rebase, base});
     expect(file.virtualPath).toBe(expected);