Index: Python/sysmodule.c
===================================================================
--- Python/sysmodule.c	(revision 64547)
+++ Python/sysmodule.c	(working copy)
@@ -651,8 +651,15 @@
 			return NULL;
 	}
 
+	/* Make sure the type is initialized.  float gets initialized late */
+	if (PyType_Ready(Py_TYPE(args)) < 0)
+		return NULL;
+
+	/* Instance of old-style classes */
+	if (PyInstance_Check(args))
+		return PyInt_FromSsize_t(PyInstance_Type.tp_basicsize);
 	/* Type objects */
-	if (PyType_Check(args)){
+	else {
 		PyObject *method = _PyType_Lookup(Py_TYPE(args),
 						  str__sizeof__);
 		if (method == NULL) {
@@ -662,15 +669,7 @@
 			return NULL;
 		}
 		return PyObject_CallFunctionObjArgs(method, args, NULL);
-	} 
-	/* Instance of old-style classes */
-	else if (PyInstance_Check(args))
-		return PyInt_FromSsize_t(PyInstance_Type.tp_basicsize);
-	/* Old-style classes */
-	else if (PyClass_Check(args))
-		return PyInt_FromSsize_t(PyClass_Type.tp_basicsize);
-	else
-		return PyObject_CallMethod(args, "__sizeof__", NULL);
+	}
 }
 
 PyDoc_STRVAR(getsizeof_doc,
Index: Lib/test/test_sys.py
===================================================================
--- Lib/test/test_sys.py	(revision 64547)
+++ Lib/test/test_sys.py	(working copy)
@@ -559,7 +559,21 @@
         self.check_sizeof((), size(h))
         self.check_sizeof((1,2,3), size(h) + 3*self.P)
 
+    def test_moduleobjects(self):
+        # Some objects from built-in modules
+        h = self.header
+        size = self.calcsize
 
+        # _sre.PatternObject
+        import re
+        x = re.compile("")
+        self.check_sizeof(x, size(h + 'P PPP PiP PH'))
+
+        # _struct.Struct
+        x = struct.Struct("")
+        self.check_sizeof(x, size(h + 'PPPPP'))
+
+
 def test_main():
     test_classes = (SysModuleTest, SizeofTest)