diff --git a/lib/util.js b/lib/util.js
index 9074e8e..ff4c851 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -21,8 +21,12 @@
 
 // NOTE: These type checking functions intentionally don't use `instanceof`
 // because it is fragile and can be easily faked with `Object.create()`.
-function isArray(ar) {
-  return Array.isArray(ar);
+
+function isArray(arg) {
+  if (Array.isArray) {
+    return Array.isArray(arg);
+  }
+  return objectToString(arg) === '[object Array]';
 }
 exports.isArray = isArray;
 
@@ -62,7 +66,7 @@ function isUndefined(arg) {
 exports.isUndefined = isUndefined;
 
 function isRegExp(re) {
-  return isObject(re) && objectToString(re) === '[object RegExp]';
+  return objectToString(re) === '[object RegExp]';
 }
 exports.isRegExp = isRegExp;
 
@@ -72,13 +76,12 @@ function isObject(arg) {
 exports.isObject = isObject;
 
 function isDate(d) {
-  return isObject(d) && objectToString(d) === '[object Date]';
+  return objectToString(d) === '[object Date]';
 }
 exports.isDate = isDate;
 
 function isError(e) {
-  return isObject(e) &&
-      (objectToString(e) === '[object Error]' || e instanceof Error);
+  return (objectToString(e) === '[object Error]' || e instanceof Error);
 }
 exports.isError = isError;
 
@@ -97,11 +100,8 @@ function isPrimitive(arg) {
 }
 exports.isPrimitive = isPrimitive;
 
-function isBuffer(arg) {
-  return Buffer.isBuffer(arg);
-}
-exports.isBuffer = isBuffer;
+exports.isBuffer = Buffer.isBuffer;
 
 function objectToString(o) {
   return Object.prototype.toString.call(o);
-}
\ No newline at end of file
+}