diff --git a/lib/buffer.js b/lib/buffer.js
index 176a8fda781..d2b87ecdb96 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -166,7 +166,7 @@ function allocPool () {
 
 // Static methods
 Buffer.isBuffer = function isBuffer(b) {
-  return b instanceof Buffer;
+  return b instanceof Buffer || b instanceof SlowBuffer;
 };