diff --git a/lib/internal/util.js b/lib/internal/util.js
index 76ef759cefbc83..cc6a7be3104175 100644
--- a/lib/internal/util.js
+++ b/lib/internal/util.js
@@ -96,11 +96,8 @@ exports.decorateErrorStack = function decorateErrorStack(err) {
 };
 
 exports.isError = function isError(e) {
-  return exports.objectToString(e) === '[object Error]' || e instanceof Error;
-};
-
-exports.objectToString = function objectToString(o) {
-  return Object.prototype.toString.call(o);
+  return Object.prototype.toString.call(e) === '[object Error]' ||
+         e instanceof Error;
 };
 
 const noCrypto = !process.versions.openssl;