diff --git a/src/main/scala/li/cil/oc/server/network/Network.scala b/src/main/scala/li/cil/oc/server/network/Network.scala
index f02631b83..dd5580cae 100644
--- a/src/main/scala/li/cil/oc/server/network/Network.scala
+++ b/src/main/scala/li/cil/oc/server/network/Network.scala
@@ -67,6 +67,9 @@ private class Network private(private val data: mutable.Map[String, Network.Vert
   // ----------------------------------------------------------------------- //
 
   def connect(nodeA: MutableNode, nodeB: MutableNode) = {
+    if (nodeA == null) throw new NullPointerException("nodeA")
+    if (nodeB == null) throw new NullPointerException("nodeB")
+
     if (nodeA == nodeB) throw new IllegalArgumentException(
       "Cannot connect a node to itself.")