diff --git a/src/routing/olsr/olsr-agent-impl.cc b/src/routing/olsr/olsr-agent-impl.cc
index 5d44ab5ec..f43b96a39 100644
--- a/src/routing/olsr/olsr-agent-impl.cc
+++ b/src/routing/olsr/olsr-agent-impl.cc
@@ -422,7 +422,7 @@ OlsrAgentImpl::MprComputation()
     {
       TwoHopNeighborTuple const &twoHopNeigh = *it;
       bool ok = true;
-      NeighborTuple *nb_tuple = m_state.FindSymNeighborTuple (twoHopNeigh.neighborMainAddr);
+      const NeighborTuple *nb_tuple = m_state.FindSymNeighborTuple (twoHopNeigh.neighborMainAddr);
       if (nb_tuple == NULL)
         {
           ok = false;
@@ -711,7 +711,7 @@ OlsrAgentImpl::RoutingTableComputation ()
     {
       TwoHopNeighborTuple const &nb2hop_tuple = *it;
       bool ok = true;
-      NeighborTuple *nb_tuple = m_state.FindSymNeighborTuple
+      const NeighborTuple *nb_tuple = m_state.FindSymNeighborTuple
         (nb2hop_tuple.neighborMainAddr);
       if (nb_tuple == NULL)
         ok = false;
diff --git a/src/routing/olsr/olsr-state.cc b/src/routing/olsr/olsr-state.cc
index d4deaf172..e0a1aa67d 100644
--- a/src/routing/olsr/olsr-state.cc
+++ b/src/routing/olsr/olsr-state.cc
@@ -94,10 +94,10 @@ OlsrState::FindNeighborTuple (Ipv4Address const &mainAddr)
   return NULL;
 }
 
-NeighborTuple*
-OlsrState::FindSymNeighborTuple (Ipv4Address const &mainAddr)
+const NeighborTuple*
+OlsrState::FindSymNeighborTuple (Ipv4Address const &mainAddr) const
 {
-  for (NeighborSet::iterator it = m_neighborSet.begin ();
+  for (NeighborSet::const_iterator it = m_neighborSet.begin ();
        it != m_neighborSet.end (); it++)
     {
       if (it->neighborMainAddr == mainAddr && it->status == NeighborTuple::STATUS_SYM)
diff --git a/src/routing/olsr/olsr-state.h b/src/routing/olsr/olsr-state.h
index ad2c735fe..836d59c07 100644
--- a/src/routing/olsr/olsr-state.h
+++ b/src/routing/olsr/olsr-state.h
@@ -64,7 +64,7 @@ public:
     return m_neighborSet;
   }
   NeighborTuple* FindNeighborTuple (const Ipv4Address &mainAddr);
-  NeighborTuple* FindSymNeighborTuple (const Ipv4Address &mainAddr);
+  const NeighborTuple* FindSymNeighborTuple (const Ipv4Address &mainAddr) const;
   NeighborTuple* FindNeighborTuple (const Ipv4Address &mainAddr,
                                     uint8_t willingness);
   void EraseNeighborTuple (const NeighborTuple &neighborTuple);