diff --git a/helper/boost-graph-ndn-global-routing-helper.h b/helper/boost-graph-ndn-global-routing-helper.h
index f406a3e..a223a82 100644
--- a/helper/boost-graph-ndn-global-routing-helper.h
+++ b/helper/boost-graph-ndn-global-routing-helper.h
@@ -302,7 +302,7 @@
 // void
 // put (cref< std::map< ns3::Ptr<ns3::ndn::GlobalRouter>, ns3::Ptr<ns3::ndn::GlobalRouter> > > map,
 
-uint32_t
+inline uint32_t
 get (const boost::VertexIds&, ns3::Ptr<ns3::ndn::GlobalRouter> &gr)
 {
   return gr->GetId ();