diff --git a/lib/util.js b/lib/util.js
index 1b168bfd945..5addac5c3aa 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -506,7 +506,12 @@ function isFunction(arg) {
 exports.isFunction = isFunction;
 
 function isPrimitive(arg) {
-  return !(arg instanceof Object);
+  return arg === null ||
+         typeof arg === 'boolean' ||
+         typeof arg === 'number' ||
+         typeof arg === 'string' ||
+         typeof arg === 'symbol' ||  // ES6 symbol
+         typeof arg === 'undefined';
 }
 exports.isPrimitive = isPrimitive;