diff --git a/imagekit/models/fields/__init__.py b/imagekit/models/fields/__init__.py
index 2aea3ca..35c78da 100644
--- a/imagekit/models/fields/__init__.py
+++ b/imagekit/models/fields/__init__.py
@@ -11,7 +11,7 @@ class SpecHostField(SpecHost):
         # Generate a spec_id to register the spec with. The default spec id is
         # "<app>:<model>_<field>"
         if not getattr(self, 'spec_id', None):
-            spec_id = (u'%s:%s_%s' % (cls._meta.app_label,
+            spec_id = (u'%s:%s:%s' % (cls._meta.app_label,
                             cls._meta.object_name, name)).lower()
 
             # Register the spec with the id. This allows specs to be overridden