diff --git a/lib/bn.js b/lib/bn.js
index 0c41a1b..57c5bb9 100644
--- a/lib/bn.js
+++ b/lib/bn.js
@@ -520,10 +520,11 @@
     return this.toString(16, 2);
   };
 
-  BN.prototype.toBuffer = function toBuffer (endian, length) {
-    assert(typeof Buffer !== 'undefined');
-    return this.toArrayLike(Buffer, endian, length);
-  };
+  if (Buffer) {
+    BN.prototype.toBuffer = function toBuffer (endian, length) {
+      return this.toArrayLike(Buffer, endian, length);
+    };
+  }
 
   BN.prototype.toArray = function toArray (endian, length) {
     return this.toArrayLike(Array, endian, length);