Index: /trunk/src/VBox/Main/src-server/NATEngineImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/src-server/NATEngineImpl.cpp	(revision 35576)
+++ /trunk/src/VBox/Main/src-server/NATEngineImpl.cpp	(revision 35577)
@@ -291,5 +291,6 @@
                             tr("A NAT rule of this name already exists"));
         if (   r.strHostIP == Utf8Str(aBindIp)
-            && r.u16HostPort == aHostPort)
+            && r.u16HostPort == aHostPort
+            && r.proto == aProto)
             return setError(E_INVALIDARG,
                             tr("A NAT rule for this host port and this host IP already exists"));