--- a/misc/migration/3.12.0_Any.py	Mon Jun 20 12:55:40 2011 +0200
+++ b/misc/migration/3.12.0_Any.py	Mon Jun 20 14:49:00 2011 +0200
@@ -1,2 +1,4 @@
-add_entity_type('TZDatetime')
-add_entity_type('TZTime')
+if schema['TZDatetime'].eid is None:
+    add_entity_type('TZDatetime')
+if schema['TZTime'].eid is None:
+    add_entity_type('TZTime')