diff --git a/.eslintrc.js b/.eslintrc.js
index 5c4933101447f2..2eb3eae6a88979 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -185,7 +185,7 @@ module.exports = {
     'no-this-before-super': 'error',
     'no-throw-literal': 'error',
     'no-trailing-spaces': 'error',
-    'no-undef': 'error',
+    'no-undef': ['error', { typeof: true }],
     'no-undef-init': 'error',
     'no-unexpected-multiline': 'error',
     'no-unreachable': 'error',
diff --git a/lib/internal/fs.js b/lib/internal/fs.js
index 6ff4152aa46814..848a11dae68a3e 100644
--- a/lib/internal/fs.js
+++ b/lib/internal/fs.js
@@ -350,7 +350,7 @@ function validateLen(len) {
   let err;
 
   if (!isInt32(len)) {
-    if (typeof value !== 'number') {
+    if (typeof len !== 'number') {
       err = new ERR_INVALID_ARG_TYPE('len', 'number', len);
     } else {
       // TODO(BridgeAR): Improve this error message.