diff --git a/planetstack/core/acl.py b/planetstack/core/acl.py
index 7856414..5b02055 100644
--- a/planetstack/core/acl.py
+++ b/planetstack/core/acl.py
@@ -16,6 +16,7 @@
     deny user scott@onlab.us
     allow user *@onlab.us
 """
+class ACLValidationError(Exception): pass
 
 class AccessControlList:
     def __init__(self, aclText=None):