diff --git a/README b/README
index 0ddc915..f5c1be0 100644
--- a/README
+++ b/README
@@ -150,7 +150,7 @@
 ndn.ChildSelector= non-negative int
 ndn.AnswerOriginKind= non-negative int
 ndn.Scope= non-negative int
-ndn.InterestLifetime= non-negative int
+ndn.InterestLifetime= non-negative int (milliseconds)
 ndn.PublisherPublicKeyDigest= % escaped value
 ndn.Nonce= % escaped value