diff --git a/tools/libxl/gentest.py b/tools/libxl/gentest.py
index 05e77cce5e..ac7a400060 100644
--- a/tools/libxl/gentest.py
+++ b/tools/libxl/gentest.py
@@ -56,6 +56,8 @@ def gen_rand_init(ty, v, indent = "    ", parent = None):
         s += "%s = rand() %% 2;\n" % v
     elif ty.typename in ["char *"]:
         s += "%s = rand_str();\n" % v
+    elif ty.private:
+        pass
     elif ty.typename in handcoded:
         raise Exception("Gen for handcoded %s" % ty.typename)
     else:
diff --git a/tools/libxl/libxltypes.py b/tools/libxl/libxltypes.py
index 55056c2750..450de88f49 100644
--- a/tools/libxl/libxltypes.py
+++ b/tools/libxl/libxltypes.py
@@ -33,6 +33,8 @@ class Type(object):
         if self.passby not in [PASS_BY_VALUE, PASS_BY_REFERENCE]:
             raise ValueError
 
+        self.private = kwargs.setdefault('private', False)
+
         if typename is None: # Anonymous type
             self.typename = None
             self.rawname = None
@@ -50,7 +52,7 @@ class Type(object):
 
         self.autogenerate_dispose_fn = kwargs.setdefault('autogenerate_dispose_fn', True)
 
-        if self.typename is not None:
+        if self.typename is not None and not self.private:
             self.json_fn = kwargs.setdefault('json_fn', self.typename + "_gen_json")
         else:
             self.json_fn = kwargs.setdefault('json_fn', None)
diff --git a/tools/python/genwrap.py b/tools/python/genwrap.py
index d0c193d26f..a5febeeab1 100644
--- a/tools/python/genwrap.py
+++ b/tools/python/genwrap.py
@@ -129,6 +129,8 @@ static PyObject *Py%(rawname)s_new(PyTypeObject *type, PyObject *args, PyObject
 
     l.append('static PyGetSetDef Py%s_getset[] = {'%ty.rawname)
     for f in ty.fields:
+        if f.type.private:
+            continue
         l.append('    { .name = "%s", '%f.name)
         if ty.marshal_out():
             l.append('      .get = (getter)py_%s_%s_get, '%(ty.rawname, f.name))
@@ -295,9 +297,13 @@ _hidden int genwrap__ll_set(PyObject *v, long long *val, long long mask);
 
 """ % tuple((' '.join(sys.argv),) + (os.path.split(decls)[-1:]),))
     for ty in types:
+        if ty.private:
+            continue
         if isinstance(ty, libxltypes.Aggregate):
             f.write('/* Attribute get/set functions for %s */\n'%ty.typename)
             for a in ty.fields:
+                if a.type.private:
+                    continue
                 if ty.marshal_out():
                     f.write(py_attrib_get(ty,a))
                 if ty.marshal_in():