diff --git a/nsync/sync-socket.cc b/nsync/sync-socket.cc
index 68eaa7d..ef6b9fb 100644
--- a/nsync/sync-socket.cc
+++ b/nsync/sync-socket.cc
@@ -112,13 +112,15 @@
   m_face->expressInterest(interest,
                           bind(&SyncSocket::onData, this, _1, _2,
                                onValidated, onValidationFailed),
+                          bind(&SyncSocket::onDataTimeout, this, _1, retry, // Nack
+                               onValidated, onValidationFailed),
                           bind(&SyncSocket::onDataTimeout, this, _1, retry,
                                onValidated, onValidationFailed));
 
 }
 
 void
-SyncSocket::onData(const ndn::Interest& interest, Data& data,
+SyncSocket::onData(const ndn::Interest& interest, const Data& data,
                    const OnDataValidated& onValidated,
                    const OnDataValidationFailed& onValidationFailed)
 {
@@ -145,6 +147,12 @@
                                    _1,
                                    retry - 1,
                                    onValidated,
+                                   onValidationFailed),
+                              bind(&SyncSocket::onDataTimeout,
+                                   this,
+                                   _1,
+                                   retry - 1,
+                                   onValidated,
                                    onValidationFailed));
 
     }