diff --git a/lib/nerves_network/if_supervisor.ex b/lib/nerves_network/if_supervisor.ex
index f54538c..d30634c 100644
--- a/lib/nerves_network/if_supervisor.ex
+++ b/lib/nerves_network/if_supervisor.ex
@@ -57,6 +57,9 @@ defmodule Nerves.Network.IFSupervisor do
       :static -> Nerves.Network.StaticManager
       :linklocal -> Nerves.Network.LinkLocalManager
       :dhcp -> Nerves.Network.DHCPManager
+
+      # Default to DHCP if unset; crash if anything else.
+      nil -> Nerves.Network.DHCPManager
     end
   end
   defp manager(:wireless, _settings) do