diff --git a/lib/fs.js b/lib/fs.js
index 89c005375f450e..16ce9450ea02ca 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -415,7 +415,7 @@ 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;
   }
@@ -808,7 +808,7 @@ function readdirSync(path, options) {
 }
 
 function fstat(fd, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }
@@ -819,7 +819,7 @@ function fstat(fd, options, callback) {
 }
 
 function lstat(path, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }
@@ -832,7 +832,7 @@ function lstat(path, options, callback) {
 }
 
 function stat(path, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }