diff --git a/src/internet/model/global-router-interface.cc b/src/internet/model/global-router-interface.cc
index 81e96626f..e976b186e 100644
--- a/src/internet/model/global-router-interface.cc
+++ b/src/internet/model/global-router-interface.cc
@@ -661,8 +661,8 @@ GlobalRouter::DiscoverLSAs()
         // associated with a bridge.  We are only going to involve devices with
         // IP addresses in routing.
         //
-        uint32_t interfaceNumber = ipv4Local->GetInterfaceForDevice(ndLocal);
-        if (!(ipv4Local->IsUp(interfaceNumber) && ipv4Local->IsForwarding(interfaceNumber)))
+        int32_t interfaceNumber = ipv4Local->GetInterfaceForDevice(ndLocal);
+        if (interfaceNumber == -1 || !(ipv4Local->IsUp(interfaceNumber) && ipv4Local->IsForwarding(interfaceNumber)))
         {
             NS_LOG_LOGIC("Net device "
                          << ndLocal