diff --git a/src/internet/model/global-route-manager-impl.cc b/src/internet/model/global-route-manager-impl.cc
index ab138f1b6..fcd942b96 100644
--- a/src/internet/model/global-route-manager-impl.cc
+++ b/src/internet/model/global-route-manager-impl.cc
@@ -837,6 +837,7 @@ GlobalRouteManagerImpl::SPFNext (SPFVertex* v, CandidateQueue& candidate)
 //
       if (v->GetLSA ()->GetLSType () == GlobalRoutingLSA::RouterLSA)
         {
+          NS_ASSERT (l != 0);
           distance = v->GetDistanceFromRoot () + l->GetMetric ();
         }
       else