diff --git a/wcs/workflows.py b/wcs/workflows.py
index ef97419e3..5f3e4ca7f 100644
--- a/wcs/workflows.py
+++ b/wcs/workflows.py
@@ -1672,7 +1672,7 @@ class WorkflowStatus(object):
                 continue
             if not action.identifier:
                 continue
-            roles = action.by
+            roles = action.by or []
             functions = [x for x in roles if x in (self.parent.roles or [])]
             roles = [x for x in roles if x not in (self.parent.roles or [])]
             if functions or roles: