diff --git a/lib/fs.js b/lib/fs.js
index ef516a218c7052..a717d794345698 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -418,7 +418,7 @@ function open(path, flags, mode, callback) {
     callback = flags;
     flags = 'r';
     mode = 0o666;
-  } else if (arguments.length === 3) {
+  } else if (typeof mode === 'function') {
     callback = mode;
     mode = 0o666;
   }
@@ -811,7 +811,7 @@ function readdirSync(path, options) {
 }
 
 function fstat(fd, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }
@@ -822,7 +822,7 @@ function fstat(fd, options, callback) {
 }
 
 function lstat(path, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }
@@ -835,7 +835,7 @@ function lstat(path, options, callback) {
 }
 
 function stat(path, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }