diff --git a/platypush/event/hook.py b/platypush/event/hook.py
index 1d428e36d..7dc3140a6 100644
--- a/platypush/event/hook.py
+++ b/platypush/event/hook.py
@@ -63,7 +63,7 @@ class EventCondition(object):
         else:
             rule = parse(rule)
 
-        assert isinstance(rule, dict)
+        assert isinstance(rule, dict), f'Not a valid rule: {rule}'
         type = get_event_class_by_type(
             rule.pop('type') if 'type' in rule else 'Event')