diff --git a/ndn-cpp/key-chain.hpp b/ndn-cpp/key-chain.hpp
index 2259064..1ddaa91 100644
--- a/ndn-cpp/key-chain.hpp
+++ b/ndn-cpp/key-chain.hpp
@@ -15,7 +15,8 @@
   /**
    * In data, set the signed info publisher public key digest and key locator key to the default public key and set the 
    * signature using the default private key.
-   * Note: the caller must make sure the timestamp is correct with data.getSignedInfo().setTimestampMilliseconds.
+   * Note: the caller must make sure the timestamp is correct, for example with 
+   * data.getSignedInfo().setTimestampMilliseconds(time(NULL) * 1000.0).
    * @param data The Data object to sign and set the signature.
    */
   static void defaultSign(Data &data);