diff --git a/src/core/thread/mesh_forwarder.cpp b/src/core/thread/mesh_forwarder.cpp
index 0776d6f52..49d24a0d0 100644
--- a/src/core/thread/mesh_forwarder.cpp
+++ b/src/core/thread/mesh_forwarder.cpp
@@ -521,9 +521,10 @@ ThreadError MeshForwarder::UpdateIp6Route(Message &aMessage)
             else
             {
                 mNetworkData.RouteLookup(ip6Header.GetSource(), ip6Header.GetDestination(), NULL, &mMeshDest);
-                assert(mMeshDest != Mac::kShortAddrInvalid);
             }
 
+            VerifyOrExit(mMeshDest != Mac::kShortAddrInvalid, error = kThreadError_Drop);
+
             if (mMle.GetNeighbor(mMeshDest) != NULL)
             {
                 // destination is neighbor