diff --git a/gns3server/schemas/dynamips_vm.py b/gns3server/schemas/dynamips_vm.py
index 96c4d81c..1ec43c62 100644
--- a/gns3server/schemas/dynamips_vm.py
+++ b/gns3server/schemas/dynamips_vm.py
@@ -140,7 +140,7 @@ VM_CREATE_SCHEMA = {
         },
         "aux": {
             "description": "Auxiliary console TCP port",
-            "type": "integer",
+            "type": ["null", "integer"],
             "minimum": 1,
             "maximum": 65535
         },