diff --git a/lib/buffer.js b/lib/buffer.js
index 57d6cddbaa2e6b..5722103fefbfd4 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -738,16 +738,15 @@ function byteLength(string, encoding) {
   }
 
   const len = string.length;
-  const mustMatch = (arguments.length > 2 && arguments[2] === true);
-  if (!mustMatch && len === 0)
+  if (len === 0)
     return 0;
 
   if (!encoding)
-    return (mustMatch ? -1 : byteLengthUtf8(string));
+    return byteLengthUtf8(string);
 
   const ops = getEncodingOps(encoding);
   if (ops === undefined)
-    return (mustMatch ? -1 : byteLengthUtf8(string));
+    return byteLengthUtf8(string);
   return ops.byteLength(string);
 }
 
diff --git a/test/parallel/test-buffer-bytelength.js b/test/parallel/test-buffer-bytelength.js
index 33cbb3268440a1..e7df93967d5b84 100644
--- a/test/parallel/test-buffer-bytelength.js
+++ b/test/parallel/test-buffer-bytelength.js
@@ -23,7 +23,7 @@ const vm = require('vm');
   );
 });
 
-assert.strictEqual(Buffer.byteLength('', undefined, true), -1);
+assert.strictEqual(Buffer.byteLength(''), 0);
 
 assert(ArrayBuffer.isView(new Buffer(10)));
 assert(ArrayBuffer.isView(new SlowBuffer(10)));