diff --git a/js/ndnProtocol/modules/ndn-js-header.txt b/js/ndnProtocol/modules/ndn-js-header.txt
index 2517732..e30c261 100644
--- a/js/ndnProtocol/modules/ndn-js-header.txt
+++ b/js/ndnProtocol/modules/ndn-js-header.txt
@@ -1,6 +1,7 @@
 /* This file is created by running make-ndn-js.jsm.sh in this directory.
  * It concatenates ndn-js-header.txt with all the ndn-js source files to
  *   make ndn-js.jsm .
+ * The file ../../tools/build/ndn-js.js must already be built.
  * author: Jeff Thompson
  * See COPYING for copyright and distribution information.
  */