diff --git a/lib/fs.js b/lib/fs.js
index 56421924fd287a..8d2c1dca628a2b 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -408,7 +408,7 @@ function open(path, flags, mode, callback) {
   path = toPathIfFileURL(path);
   validatePath(path);
   const flagsNumber = stringToFlags(flags);
-  if (arguments.length < 4) {
+  if (typeof mode === 'function') {
     callback = makeCallback(mode);
     mode = 0o666;
   } else {
@@ -788,7 +788,7 @@ function readdirSync(path, options) {
 }
 
 function fstat(fd, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }
@@ -799,7 +799,7 @@ function fstat(fd, options, callback) {
 }
 
 function lstat(path, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }
@@ -812,7 +812,7 @@ function lstat(path, options, callback) {
 }
 
 function stat(path, options, callback) {
-  if (arguments.length < 3) {
+  if (typeof options === 'function') {
     callback = options;
     options = {};
   }