diff --git a/model/ccnx-content-store.cc b/model/ccnx-content-store.cc
index 9232ebc..4875386 100644
--- a/model/ccnx-content-store.cc
+++ b/model/ccnx-content-store.cc
@@ -150,7 +150,7 @@
 }
 
 
-boost::tuple<Ptr<Packet>, Ptr<CcnxContentObjectHeader> >
+boost::tuple<Ptr<Packet>, Ptr<const CcnxContentObjectHeader> >
 CcnxContentStore::Lookup (Ptr<const CcnxInterestHeader> interest)
 {
   NS_LOG_FUNCTION_NOARGS ();