diff --git a/boto/mturk/notification.py b/boto/mturk/notification.py
index 3cd4d24319..2aa99ca47b 100644
--- a/boto/mturk/notification.py
+++ b/boto/mturk/notification.py
@@ -85,7 +85,8 @@ def __init__(self, d):
         self.event_time_str = d['EventTime']
         self.hit_type = d['HITTypeId']
         self.hit_id = d['HITId']
-        self.assignment_id = d['AssignmentId']
+        if 'AssignmentId' in d:   # Not present in all event types
+            self.assignment_id = d['AssignmentId']
 
         #TODO: build self.event_time datetime from string self.event_time_str