diff --git a/qubes/__init__.py b/qubes/__init__.py
index 9e7344a4..1a805cc6 100644
--- a/qubes/__init__.py
+++ b/qubes/__init__.py
@@ -1072,6 +1072,10 @@ class VMProperty(property):
 
 
     def __set__(self, instance, value):
+        if value is self.__class__.DEFAULT:
+            self.__delete__(instance)
+            return
+
         if value == self._none_value:
             value = None
         if value is None: