diff --git a/ndn-cpp/helpers/hash.h b/ndn-cpp/helpers/hash.h
index 1652f2b..8ac23fa 100644
--- a/ndn-cpp/helpers/hash.h
+++ b/ndn-cpp/helpers/hash.h
@@ -25,6 +25,7 @@
 
 class Hash;
 typedef boost::shared_ptr<Hash> HashPtr;
+typedef boost::shared_ptr<const Hash> ConstHashPtr;
 
 class Hash
 {