diff --git a/lib/reporters/base.js b/lib/reporters/base.js
index 5af6e7bd8a..6dd18a64ee 100644
--- a/lib/reporters/base.js
+++ b/lib/reporters/base.js
@@ -230,7 +230,7 @@ var generateDiff = (exports.generateDiff = function (actual, expected) {
  * @return {{ message: string, msg: string, stack: string }}
  */
 var getFullErrorStack = function (err, seen) {
-  if (seen && seen.has(err)) {
+  if (seen?.has(err)) {
     return { message: '', msg: '<circular>', stack: '' };
   }
 
diff --git a/lib/runner.js b/lib/runner.js
index 60a19f0e3f..87b4b8c3a4 100644
--- a/lib/runner.js
+++ b/lib/runner.js
@@ -448,7 +448,7 @@ Runner.prototype.fail = function (test, err, force) {
     const alreadyFiltered = new Set();
     let currentErr = err;
 
-    while (currentErr && currentErr.stack && !alreadyFiltered.has(currentErr)) {
+    while (currentErr?.stack && !alreadyFiltered.has(currentErr)) {
       alreadyFiltered.add(currentErr);
 
       try {