diff --git a/django_hstore/virtual.py b/django_hstore/virtual.py
old mode 100755
new mode 100644
index 4dd9b79..e11fd2f
--- a/django_hstore/virtual.py
+++ b/django_hstore/virtual.py
@@ -14,6 +14,8 @@ class HStoreVirtualMixin(object):
     """
     must be mixed-in with django fields
     """
+    concrete = False
+    
     def contribute_to_class(self, cls, name):
         if self.choices:
             setattr(cls, 'get_%s_display' % self.name,