diff --git a/lib/buffer.js b/lib/buffer.js
index 87bdfd2d95fb7e..5450861d04e986 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -456,10 +456,7 @@ function byteLength(string, encoding) {
         return len >>> 1;
       break;
   }
-  if (mustMatch)
-    throw new TypeError('Unknown encoding: ' + encoding);
-  else
-    return binding.byteLengthUtf8(string);
+  return (mustMatch ? -1 : binding.byteLengthUtf8(string));
 }
 
 Buffer.byteLength = byteLength;
diff --git a/test/parallel/test-buffer-alloc.js b/test/parallel/test-buffer-alloc.js
index 02ed1bcf63669e..7b868f783ee997 100644
--- a/test/parallel/test-buffer-alloc.js
+++ b/test/parallel/test-buffer-alloc.js
@@ -885,7 +885,8 @@ assert.throws(() => Buffer.allocUnsafe(8).writeFloatLE(0.0, -1), RangeError);
 }
 
 // Regression test for #5482: should throw but not assert in C++ land.
-assert.throws(() => Buffer.from('', 'buffer'), TypeError);
+assert.throws(() => Buffer.from('', 'buffer'),
+              /^TypeError: "encoding" must be a valid string encoding$/);
 
 // Regression test for #6111. Constructing a buffer from another buffer
 // should a) work, and b) not corrupt the source buffer.