diff --git a/lib/_stream_readable.js b/lib/_stream_readable.js
index f4b366e9f451f8..f1469b84f254f0 100644
--- a/lib/_stream_readable.js
+++ b/lib/_stream_readable.js
@@ -327,7 +327,7 @@ Readable.prototype.setEncoding = function(enc) {
   if (!StringDecoder)
     StringDecoder = require('string_decoder').StringDecoder;
   this._readableState.decoder = new StringDecoder(enc);
-  // if setEncoding(null), decoder.encoding = 'utf8'
+  // if setEncoding(null), decoder.encoding equals utf8
   this._readableState.encoding = this._readableState.decoder.encoding;
   return this;
 };
diff --git a/test/parallel/test-stream-readable-setEncoding-null.js b/test/parallel/test-stream-readable-setEncoding-null.js
new file mode 100644
index 00000000000000..b95b26bb795728
--- /dev/null
+++ b/test/parallel/test-stream-readable-setEncoding-null.js
@@ -0,0 +1,15 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { Readable } = require('stream');
+
+
+{
+  const readable = new Readable({ encoding: 'hex' });
+  assert.strictEqual(readable._readableState.encoding, 'hex');
+
+  readable.setEncoding(null);
+
+  assert.strictEqual(readable._readableState.encoding, 'utf8');
+}