diff --git a/common/lib/xmodule/xmodule/util/misc.py b/common/lib/xmodule/xmodule/util/misc.py
index 9e3e0b83b3..3f5ba4aa2c 100644
--- a/common/lib/xmodule/xmodule/util/misc.py
+++ b/common/lib/xmodule/xmodule/util/misc.py
@@ -90,6 +90,8 @@ def get_default_short_labeler(course):
         for that assignment type, this function would return "Ex 02", assuming
         that "Ex" is the short_label assigned to a grader for Homework subsections.
         """
+        if assignment_type not in default_labelers:
+            return None
         labeler = default_labelers[assignment_type]['labeler']
         index = default_labelers[assignment_type]['index']
         default_labelers[assignment_type]['index'] += 1